Rambda

Rambda is smaller and faster alternative to the popular functional programming library Ramda. - Documentation

❯ Example use

import { compose, map, filter } from 'rambda'

const result = compose(
  map(x => x * 2),
  filter(x => x > 2)
)([1, 2, 3, 4])
// => [6, 8]

You can test this example in Rambda's REPL

Differences between Rambda and Ramda
API
Changelog

❯ Rambda's advantages

Typescript included

Typescript definitions are included in the library, in comparison to Ramda, where you need to additionally install @types/ramda.

Still, you need to be aware that functional programming features in Typescript are in development, which means that using R.compose/R.pipe can be problematic.

Important - Rambda version 7.0.0(or higher) requires Typescript version 4.2.2(or higher).

Alternative TS definitions are available as rambda/immutable. These are Rambda definitions linted with ESLint functional/prefer-readonly-type plugin.

Smaller size

The size of a library affects not only the build bundle size but also the dev bundle size and build time. This is important advantage, expecially for big projects.

Tree-shaking

Currently Rambda is more tree-shakable than Ramda - proven in the following repo.

The repo holds two Angular9 applications: one with small example code of Ramda and the other - same code but with Rambda as import library.

The test shows that Rambda bundle size is 2 MB less than its Ramda counterpart.

There is also Webpack/Rollup/Parcel/Esbuild tree-shaking example including several libraries including Ramda, Rambda and Rambdax.

actually tree-shaking is the initial reason for creation of Rambda

Dot notation for `R.path`, `R.paths`, `R.assocPath` and `R.lensPath`

Standard usage of R.path is R.path(['a', 'b'], {a: {b: 1} }).

In Rambda you have the choice to use dot notation(which is arguably more readable):

R.path('a.b', {a: {b: 1} })

Comma notation for `R.pick` and `R.omit`

Similar to dot notation, but the separator is comma(,) instead of dot(.).

R.pick('a,b', {a: 1 , b: 2, c: 3} })
// No space allowed between properties

Speed

Rambda is generally more performant than Ramda as the benchmarks can prove that.

Support

Most of the valid issues are fixed within 2-3 days.

Closing the issue is usually accompanied by publishing a new patch version of Rambda to NPM.

❯ Missing Ramda methods

Click to see the full list of 90 Ramda methods not implemented in Rambda

__
addIndex
ap
aperture
applyTo
ascend
binary
call
collectBy
comparator
composeWith
construct
constructN
count
countBy
descend
differenceWith
dissocPath
empty
eqBy
forEachObjIndexed
gt
gte
hasIn
innerJoin
insert
insertAll
into
invert
invertObj
invoker
juxt
keysIn
lift
liftN
lt
lte
mapAccum
mapAccumRight
memoizeWith
mergeDeepLeft
mergeDeepWith
mergeDeepWithKey
mergeRight
mergeWith
mergeWithKey
modify
modifyPath
nAry
partialObject
nthArg
o
on
otherwise
pair
partialRight
pathSatisfies
pickBy
pipeWith
project
promap
propSatisfies
reduceBy
reduceRight
reduceWhile
reduced
remove
scan
sequence
sortWith
splitWhenever
symmetricDifferenceWith
andThen
toPairsIn
transduce
traverse
unary
uncurryN
unfold
unionWith
uniqBy
unnest
until
unwind
useWith
valuesIn
whereAny
xprod
thunkify
default

❯ Install

yarn add rambda
For UMD usage either use ./dist/rambda.umd.js or the following CDN link:

https://unpkg.com/rambda@CURRENT_VERSION/dist/rambda.umd.js

with deno

import {compose, add} from 'https://raw.githubusercontent.com/selfrefactor/rambda/master/dist/rambda.esm.js'

Differences between Rambda and Ramda

Rambda's type detects async functions and unresolved Promises. The returned values are 'Async' and 'Promise'.
Rambda's type handles NaN input, in which case it returns NaN.
Rambda's forEach can iterate over objects not only arrays.
Rambda's map, filter, partition when they iterate over objects, they pass property and input object as predicate's argument.
Rambda's filter returns empty array with bad input(null or undefined), while Ramda throws.
Ramda's clamp work with strings, while Rambda's method work only with numbers.
Ramda's indexOf/lastIndexOf work with strings and lists, while Rambda's method work only with lists as iterable input.
Error handling, when wrong inputs are provided, may not be the same. This difference will be better documented once all brute force tests are completed.
Typescript definitions between rambda and @types/ramda may vary.

If you need more Ramda methods in Rambda, you may either submit a PR or check the extended version of Rambda - Rambdax. In case of the former, you may want to consult with Rambda contribution guidelines.

❯ Benchmarks

Click to expand all benchmark results

There are methods which are benchmarked only with Ramda and Rambda(i.e. no Lodash).

Note that some of these methods, are called with and without curring. This is done in order to give more detailed performance feedback.

The benchmarks results are produced from latest versions of Rambda, Lodash(4.17.21) and Ramda(0.27.1).

method	Rambda	Ramda	Lodash
add	🚀 Fastest	21.52% slower	82.15% slower
adjust	8.48% slower	🚀 Fastest	🔳
all	🚀 Fastest	1.81% slower	🔳
allPass	🚀 Fastest	91.09% slower	🔳
allPass	🚀 Fastest	98.56% slower	🔳
and	🚀 Fastest	89.09% slower	🔳
any	🚀 Fastest	92.87% slower	45.82% slower
anyPass	🚀 Fastest	98.25% slower	🔳
append	🚀 Fastest	2.07% slower	🔳
applySpec	🚀 Fastest	80.43% slower	🔳
assoc	72.32% slower	60.08% slower	🚀 Fastest
clone	🚀 Fastest	91.86% slower	86.48% slower
compose	🚀 Fastest	32.45% slower	13.68% slower
converge	78.63% slower	🚀 Fastest	🔳
curry	🚀 Fastest	28.86% slower	🔳
curryN	🚀 Fastest	41.05% slower	🔳
defaultTo	🚀 Fastest	48.91% slower	🔳
drop	🚀 Fastest	82.35% slower	🔳
dropLast	🚀 Fastest	86.74% slower	🔳
equals	58.37% slower	96.73% slower	🚀 Fastest
filter	6.7% slower	72.03% slower	🚀 Fastest
find	🚀 Fastest	85.14% slower	42.65% slower
findIndex	🚀 Fastest	86.48% slower	72.27% slower
flatten	🚀 Fastest	95.26% slower	10.27% slower
ifElse	🚀 Fastest	58.56% slower	🔳
includes	🚀 Fastest	84.63% slower	🔳
indexOf	🚀 Fastest	76.63% slower	🔳
indexOf	🚀 Fastest	82.2% slower	🔳
init	🚀 Fastest	92.24% slower	13.3% slower
is	🚀 Fastest	57.69% slower	🔳
isEmpty	🚀 Fastest	97.14% slower	54.99% slower
last	🚀 Fastest	93.43% slower	5.28% slower
lastIndexOf	🚀 Fastest	85.19% slower	🔳
map	🚀 Fastest	86.6% slower	11.73% slower
match	🚀 Fastest	44.83% slower	🔳
merge	🚀 Fastest	12.21% slower	55.76% slower
none	🚀 Fastest	96.48% slower	🔳
objOf	🚀 Fastest	38.05% slower	🔳
omit	🚀 Fastest	69.95% slower	97.34% slower
over	🚀 Fastest	56.23% slower	🔳
path	37.81% slower	77.81% slower	🚀 Fastest
pick	🚀 Fastest	19.07% slower	80.2% slower
pipe	0.87% slower	🚀 Fastest	🔳
prop	🚀 Fastest	87.95% slower	🔳
propEq	🚀 Fastest	91.92% slower	🔳
range	🚀 Fastest	61.8% slower	57.44% slower
reduce	60.48% slower	77.1% slower	🚀 Fastest
repeat	48.57% slower	68.98% slower	🚀 Fastest
replace	33.45% slower	33.99% slower	🚀 Fastest
set	🚀 Fastest	50.35% slower	🔳
sort	🚀 Fastest	40.23% slower	🔳
sortBy	🚀 Fastest	25.29% slower	56.88% slower
split	🚀 Fastest	55.37% slower	17.64% slower
splitEvery	🚀 Fastest	71.98% slower	🔳
take	🚀 Fastest	91.96% slower	4.72% slower
takeLast	🚀 Fastest	93.39% slower	19.22% slower
test	🚀 Fastest	82.34% slower	🔳
type	🚀 Fastest	48.6% slower	🔳
uniq	🚀 Fastest	90.24% slower	🔳
uniqWith	25.38% slower	🚀 Fastest	🔳
uniqWith	14.23% slower	🚀 Fastest	🔳
update	🚀 Fastest	52.35% slower	🔳
view	🚀 Fastest	76.15% slower	🔳

❯ Used by

API

add

add(a: number, b: number): number

It adds a and b.

💥 It doesn't work with strings, as the inputs are parsed to numbers before calculation.

R.add(2, 3) // =>  5

Try this R.add example in Rambda REPL

All Typescript definitions

add(a: number, b: number): number;
add(a: number): (b: number) => number;

R.add source

export function add(a, b) {
  if (arguments.length === 1) return _b => add(a, _b)

  return Number(a) + Number(b)
}

Tests

import {add} from './add'
import {add as addRamda} from 'ramda'
import {compareCombinations} from './_internals/testUtils'

test('with number', () => {
  expect(add(2, 3)).toEqual(5)
  expect(add(7)(10)).toEqual(17)
})

test('string is bad input', () => {
  expect(add('foo', 'bar')).toBeNaN()
})

test('ramda specs', () => {
  expect(add('1', '2')).toEqual(3)
  expect(add(1, '2')).toEqual(3)
  expect(add(true, false)).toEqual(1)
  expect(add(null, null)).toEqual(0)
  expect(add(undefined, undefined)).toEqual(NaN)
  expect(add(new Date(1), new Date(2))).toEqual(3)
})

const possibleInputs = [
  /foo/,
  'foo',
  true,
  3,
  NaN,
  4,
  [],
  Promise.resolve(1),
]

describe('brute force', () => {
  compareCombinations({
    fn: add,
    fnRamda: addRamda,
    firstInput: possibleInputs,
    secondInput: possibleInputs,
    callback: errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        Object {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 0,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 64,
        }
      `)
    },
  })
})

Typescript test

import {add} from 'rambda'

describe('R.add', () => {
  it('happy', () => {
    const result = add(4, 1)

    result // $ExpectType number
  })
  it('curried', () => {
    const result = add(4)(1)

    result // $ExpectType number
  })
})

Rambda is fastest. Ramda is 21.52% slower and Lodash is 82.15% slower

const R = require('../../dist/rambda.js')

const add = [
  {
    label: 'Rambda',
    fn: () => {
      R.add(1, 1)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.add(1, 1)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.add(1, 1)
    },
  },
]

adjust

adjust<T>(index: number, replaceFn: (x: T) => T, list: T[]): T[]

It replaces index in array list with the result of replaceFn(list[i]).

R.adjust(
  0,
  a => a + 1,
  [0, 100]
) // => [1, 100]

Try this R.adjust example in Rambda REPL

All Typescript definitions

adjust<T>(index: number, replaceFn: (x: T) => T, list: T[]): T[];
adjust<T>(index: number, replaceFn: (x: T) => T): (list: T[]) => T[];

R.adjust source

import {curry} from './curry'
import {cloneList} from './_internals/cloneList'

function adjustFn(index, replaceFn, list) {
  const actualIndex = index < 0 ? list.length + index : index
  if (index >= list.length || actualIndex < 0) return list

  const clone = cloneList(list)
  clone[actualIndex] = replaceFn(clone[actualIndex])

  return clone
}

export const adjust = curry(adjustFn)

Tests

import {add} from './add'
import {adjust} from './adjust'
import {pipe} from './pipe'

const list = [0, 1, 2]
const expected = [0, 11, 2]

test('happy', () => {})

test('happy', () => {
  expect(adjust(1, add(10), list)).toEqual(expected)
})

test('with curring type 1 1 1', () => {
  expect(adjust(1)(add(10))(list)).toEqual(expected)
})

test('with curring type 1 2', () => {
  expect(adjust(1)(add(10), list)).toEqual(expected)
})

test('with curring type 2 1', () => {
  expect(adjust(1, add(10))(list)).toEqual(expected)
})

test('with negative index', () => {
  expect(adjust(-2, add(10), list)).toEqual(expected)
})

test('when index is out of bounds', () => {
  const list = [0, 1, 2, 3]
  expect(adjust(4, add(1), list)).toEqual(list)
  expect(adjust(-5, add(1), list)).toEqual(list)
})

Rambda is slower than Ramda with 8.48%

const R = require('../../dist/rambda.js')

const list = [0, 1, 2]
const fn = x => x + 1
const index = 1

const adjust = [
  {
    label: 'Rambda',
    fn: () => {
      R.adjust(index, fn, list)
      R.adjust(index, fn)(list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.adjust(index, fn, list)
      Ramda.adjust(index, fn)(list)
    },
  },
]

all

all<T>(predicate: (x: T) => boolean, list: T[]): boolean

It returns true, if all members of array list returns true, when applied as argument to predicate function.

const list = [ 0, 1, 2, 3, 4 ]
const predicate = x => x > -1

const result = R.all(predicate, list)
// => true

Try this R.all example in Rambda REPL

All Typescript definitions

all<T>(predicate: (x: T) => boolean, list: T[]): boolean;
all<T>(predicate: (x: T) => boolean): (list: T[]) => boolean;

R.all source

export function all(predicate, list) {
  if (arguments.length === 1) return _list => all(predicate, _list)

  for (let i = 0; i < list.length; i++) {
    if (!predicate(list[i])) return false
  }

  return true
}

Tests

import {all} from './all'

const list = [0, 1, 2, 3, 4]

test('when true', () => {
  const fn = x => x > -1

  expect(all(fn)(list)).toBeTrue()
})

test('when false', () => {
  const fn = x => x > 2

  expect(all(fn, list)).toBeFalse()
})

Typescript test

import {all} from 'rambda'

describe('all', () => {
  it('happy', () => {
    const result = all(
      x => {
        x // $ExpectType number
        return x > 0
      },
      [1, 2, 3]
    )
    result // $ExpectType boolean
  })
  it('curried needs a type', () => {
    const result = all<number>(x => {
      x // $ExpectType number
      return x > 0
    })([1, 2, 3])
    result // $ExpectType boolean
  })
})

Rambda is faster than Ramda with 1.81%

const R = require('../../dist/rambda.js')

const {
  uniqListOfObjects,
  uniqListOfStrings,
  rangeOfNumbers,
  uniqListOfLists,
} = require('./_utils.js')

const limit = 100

const modes = [
  [uniqListOfObjects(limit), x => Object.keys(x).length > 2],
  [uniqListOfStrings(limit), x => x.length > 0],
  [uniqListOfLists(limit), x => x.length > 0],
  [rangeOfNumbers(limit), x => x > -1],
]

const applyBenchmark = (fn, input) => {
  return fn(input[1], input[0])
}

const tests = [
  {
    label: 'Rambda',
    fn: R.all,
  },
  {
    label: 'Ramda',
    fn: Ramda.all,
  },
]

allPass

allPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean

It returns true, if all functions of predicates return true, when input is their argument.

const input = {
  a : 1,
  b : 2,
}
const predicates = [
  x => x.a === 1,
  x => x.b === 2,
]
const result = R.allPass(predicates)(input) // => true

Try this R.allPass example in Rambda REPL

All Typescript definitions

allPass<T>(predicates: ((x: T) => boolean)[]): (input: T) => boolean;

R.allPass source

export function allPass(predicates) {
  return (...input) => {
    let counter = 0
    while (counter < predicates.length) {
      if (!predicates[counter](...input)) {
        return false
      }
      counter++
    }

    return true
  }
}

Tests

import {allPass} from './allPass'

test('happy', () => {
  const rules = [x => typeof x === 'number', x => x > 10, x => x * 7 < 100]

  expect(allPass(rules)(11)).toBeTrue()

  expect(allPass(rules)(undefined)).toBeFalse()
})

test('when returns true', () => {
  const conditionArr = [val => val.a === 1, val => val.b === 2]

  expect(
    allPass(conditionArr)({
      a: 1,
      b: 2,
    })
  ).toBeTrue()
})

test('when returns false', () => {
  const conditionArr = [val => val.a === 1, val => val.b === 3]

  expect(
    allPass(conditionArr)({
      a: 1,
      b: 2,
    })
  ).toBeFalse()
})

test('works with multiple inputs', () => {
  var fn = function (w, x, y, z) {
    return w + x === y + z
  }
  expect(allPass([fn])(3, 3, 3, 3)).toBeTrue()
})

Typescript test

import {allPass} from 'rambda'

describe('allPass', () => {
  it('happy', () => {
    const x = allPass<number>([
      y => {
        y // $ExpectType number
        return typeof y === 'number'
      },
      y => {
        return y > 0
      },
    ])(11)

    x // $ExpectType boolean
  })
})

Rambda is faster than Ramda with 91.09%

const R = require('../../dist/rambda.js')

const {random} = require('rambdax')

const limit = 100
const min = 10
const max = 1200
function createListOfFunctions(fn, fnLimit) {
  return Array(fnLimit)
    .fill(null)
    .map(() => fn())
}

const modes = [
  [
    {foo: 1500},
    createListOfFunctions(
      () => x => Number(x.foo) > random(min, max),
      limit
    ),
  ],
  [
    '1500',
    createListOfFunctions(() => x => Number(x) > random(min, max), limit),
  ],
  [
    [1, 2, 1500],
    createListOfFunctions(() => x => x[2] > random(min, max), limit),
  ],
  [1500, createListOfFunctions(() => x => x > random(min, max), limit)],
]

const applyBenchmark = (fn, input) => {
  return fn(input[1])(input[0])
}
const tests = [
  {
    label: 'Rambda',
    fn: R.allPass,
  },
  {
    label: 'Ramda',
    fn: Ramda.allPass,
  },
]

always

always<T>(x: T): (...args: unknown[]) => T

It returns function that always returns x.

const fn = R.always(7)

const result = fn()
// => 7

Try this R.always example in Rambda REPL

All Typescript definitions

always<T>(x: T): (...args: unknown[]) => T;

R.always source

export function always(x) {
  return () => x
}

Tests

import {always} from './always'
import {F} from './F'

test('happy', () => {
  const fn = always(7)

  expect(fn()).toEqual(7)
  expect(fn()).toEqual(7)
})

test('f', () => {
  const fn = always(F())

  expect(fn()).toBeFalse()
  expect(fn()).toBeFalse()
})

Typescript test

import {always} from 'rambda'

describe('R.always', () => {
  it('happy', () => {
    const fn = always('foo')
    fn // $ExpectType (...args: unknown[]) => string
    const result = fn()
    result // $ExpectType string
  })
})

and

Logical AND

R.and(true, true); // => true
R.and(false, true); // => false
R.and(true, 'foo'); // => 'foo'

Try this R.and example in Rambda REPL

any

any<T>(predicate: (x: T) => boolean, list: T[]): boolean

It returns true, if at least one member of list returns true, when passed to a predicate function.

const list = [1, 2, 3]
const predicate = x => x * x > 8
R.any(fn, list)
// => true

Try this R.any example in Rambda REPL

All Typescript definitions

any<T>(predicate: (x: T) => boolean, list: T[]): boolean;
any<T>(predicate: (x: T) => boolean): (list: T[]) => boolean;

R.any source

export function any(predicate, list) {
  if (arguments.length === 1) return _list => any(predicate, _list)

  let counter = 0
  while (counter < list.length) {
    if (predicate(list[counter], counter)) {
      return true
    }
    counter++
  }

  return false
}

Tests

import {any} from './any'

const list = [1, 2, 3]

test('happy', () => {
  expect(any(x => x < 0, list)).toBeFalse()
})

test('with curry', () => {
  expect(any(x => x > 2)(list)).toBeTrue()
})

Typescript test

import {any} from 'rambda'

describe('R.any', () => {
  it('happy', () => {
    const result = any(
      x => {
        x // $ExpectType number
        return x > 2
      },
      [1, 2, 3]
    )
    result // $ExpectType boolean
  })

  it('when curried needs a type', () => {
    const result = any<number>(x => {
      x // $ExpectType number
      return x > 2
    })([1, 2, 3])
    result // $ExpectType boolean
  })
})

Rambda is fastest. Ramda is 92.87% slower and Lodash is 45.82% slower

const R = require('../../dist/rambda.js')

const input = [1, 2, 3, 4]
const fn = val => val > 2

const any = [
  {
    label: 'Rambda',
    fn: () => {
      R.any(fn, input)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.any(fn, input)
    },
  },
  {
    label: 'Lodash.some',
    fn: () => {
      _.some(input, fn)
    },
  },
]

anyPass

anyPass<T>(predicates: SafePred<T>[]): SafePred<T>

It accepts list of predicates and returns a function. This function with its input will return true, if any of predicates returns true for this input.

const isBig = x => x > 20
const isOdd = x => x % 2 === 1
const input = 11

const fn = R.anyPass(
  [isBig, isOdd]
)

const result = fn(input) 
// => true

Try this R.anyPass example in Rambda REPL

All Typescript definitions

anyPass<T>(predicates: SafePred<T>[]): SafePred<T>;

R.anyPass source

export function anyPass(predicates) {
  return (...input) => {
    let counter = 0
    while (counter < predicates.length) {
      if (predicates[counter](...input)) {
        return true
      }
      counter++
    }

    return false
  }
}

Tests

import {anyPass} from './anyPass'

test('happy', () => {
  const rules = [x => typeof x === 'string', x => x > 10]
  const predicate = anyPass(rules)
  expect(predicate('foo')).toBeTrue()
  expect(predicate(6)).toBeFalse()
})

test('happy', () => {
  const rules = [x => typeof x === 'string', x => x > 10]

  expect(anyPass(rules)(11)).toBeTrue()

  expect(anyPass(rules)(undefined)).toBeFalse()
})

const obj = {
  a: 1,
  b: 2,
}

test('when returns true', () => {
  const conditionArr = [val => val.a === 1, val => val.a === 2]

  expect(anyPass(conditionArr)(obj)).toBeTrue()
})

test('when returns false + curry', () => {
  const conditionArr = [val => val.a === 2, val => val.b === 3]

  expect(anyPass(conditionArr)(obj)).toBeFalse()
})

test('with empty predicates list', () => {
  expect(anyPass([])(3)).toEqual(false)
})

test('works with multiple inputs', () => {
  var fn = function (w, x, y, z) {
    console.log(w, x, y, z)
    return w + x === y + z
  }
  expect(anyPass([fn])(3, 3, 3, 3)).toBeTrue()
})

Typescript test

import {anyPass} from 'rambda'

describe('anyPass', () => {
  it('happy', () => {
    const x = anyPass<number>([
      y => {
        y // $ExpectType number
        return typeof y === 'number'
      },
      y => {
        return y > 0
      },
    ])(11)

    x // $ExpectType boolean
  })
})

Rambda is faster than Ramda with 98.25%

const R = require('../../dist/rambda.js')

const rules = [x => typeof x === 'boolean', x => x > 20, x => x * 7 < 100]

const anyPass = [
  {
    label: 'Rambda',
    fn: () => {
      R.anyPass(rules)(11)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.anyPass(rules)(11)
    },
  },
]

append

append<T>(x: T, list: T[]): T[]

It adds element x at the end of list.

const x = 'foo'

const result = R.append(x, ['bar', 'baz'])
// => ['bar', 'baz', 'foo']

Try this R.append example in Rambda REPL

All Typescript definitions

append<T>(x: T, list: T[]): T[];
append<T>(x: T): <T>(list: T[]) => T[];

R.append source

import {cloneList} from './_internals/cloneList'

export function append(x, input) {
  if (arguments.length === 1) return _input => append(x, _input)

  if (typeof input === 'string') return input.split('').concat(x)

  const clone = cloneList(input)
  clone.push(x)

  return clone
}

Tests

import {append} from './append'

test('happy', () => {
  expect(append('tests', ['write', 'more'])).toEqual([
    'write',
    'more',
    'tests',
  ])
})

test('append to empty array', () => {
  expect(append('tests')([])).toEqual(['tests'])
})

test('with strings', () => {
  expect(append('o', 'fo')).toEqual(['f', 'o', 'o'])
})

Typescript test

import {append} from 'rambda'

const list = [1, 2, 3]

describe('R.append', () => {
  it('happy', () => {
    const result = append(4, list)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = append(4)(list)

    result // $ExpectType number[]
  })
})

Rambda is faster than Ramda with 2.07%

const R = require('../../dist/rambda.js')

const append = [
  {
    label: 'Rambda',
    fn: () => {
      R.append(0)([1, 2, 3, 4])
      R.append('bar')('foo')
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.append(0)([1, 2, 3, 4])
      Ramda.append('bar')('foo')
    },
  },
]

apply

apply<T = any>(fn: (...args: any[]) => T, args: any[]): T

It applies function fn to the list of arguments.

This is useful for creating a fixed-arity function from a variadic function. fn should be a bound function if context is significant.

const result = R.apply(Math.max, [42, -Infinity, 1337])
// => 1337

Try this R.apply example in Rambda REPL

All Typescript definitions

apply<T = any>(fn: (...args: any[]) => T, args: any[]): T;
apply<T = any>(fn: (...args: any[]) => T): (args: any[]) => T;

R.apply source

export function apply(fn, args) {
  if (arguments.length === 1) {
    return _args => apply(fn, _args)
  }

  return fn.apply(this, args)
}

Tests

import {apply} from './apply'
import {bind} from './bind'
import {identity} from './identity'

test('happy', () => {
  expect(apply(identity, [1, 2, 3])).toEqual(1)
})

test('applies function to argument list', function () {
  expect(apply(Math.max, [1, 2, 3, -99, 42, 6, 7])).toEqual(42)
})

test('provides no way to specify context', function () {
  const obj = {
    method: function () {
      return this === obj
    },
  }
  expect(apply(obj.method, [])).toEqual(false)
  expect(apply(bind(obj.method, obj), [])).toEqual(true)
})

Typescript test

import {apply, identity} from 'rambda'

describe('R.apply', () => {
  it('happy', () => {
    const result = apply<number>(identity, [1, 2, 3])

    result // $ExpectType number
  })
  it('curried', () => {
    const fn = apply<number>(identity)
    const result = fn([1, 2, 3])

    result // $ExpectType number
  })
})

applySpec

applySpec<Spec extends Record<string, (...args: any[]) => any>>(
  spec: Spec
): (
  ...args: Parameters<ValueOfRecord<Spec>>
) => { [Key in keyof Spec]: ReturnType<Spec[Key]> }

💥 The currying in this function works best with functions with 4 arguments or less. (arity of 4)

const fn = R.applySpec({
  sum: R.add,
  nested: { mul: R.multiply }
})
const result = fn(2, 4) 
// => { sum: 6, nested: { mul: 8 } }

Try this R.applySpec example in Rambda REPL

All Typescript definitions

applySpec<Spec extends Record<string, (...args: any[]) => any>>(
  spec: Spec
): (
  ...args: Parameters<ValueOfRecord<Spec>>
) => { [Key in keyof Spec]: ReturnType<Spec[Key]> };
applySpec<T>(spec: any): (...args: any[]) => T;

R.applySpec source

import {_isArray} from './_internals/_isArray'

// recursively traverse the given spec object to find the highest arity function
function __findHighestArity(spec, max = 0) {
  for (const key in spec) {
    if (spec.hasOwnProperty(key) === false || key === 'constructor') continue

    if (typeof spec[key] === 'object') {
      max = Math.max(max, __findHighestArity(spec[key]))
    }

    if (typeof spec[key] === 'function') {
      max = Math.max(max, spec[key].length)
    }
  }

  return max
}

function __filterUndefined() {
  const defined = []
  let i = 0
  const l = arguments.length
  while (i < l) {
    if (typeof arguments[i] === 'undefined') break
    defined[i] = arguments[i]
    i++
  }

  return defined
}

function __applySpecWithArity(spec, arity, cache) {
  const remaining = arity - cache.length

  if (remaining === 1)
    return x =>
      __applySpecWithArity(spec, arity, __filterUndefined(...cache, x))
  if (remaining === 2)
    return (x, y) =>
      __applySpecWithArity(spec, arity, __filterUndefined(...cache, x, y))
  if (remaining === 3)
    return (x, y, z) =>
      __applySpecWithArity(spec, arity, __filterUndefined(...cache, x, y, z))
  if (remaining === 4)
    return (x, y, z, a) =>
      __applySpecWithArity(
        spec,
        arity,
        __filterUndefined(...cache, x, y, z, a)
      )
  if (remaining > 4)
    return (...args) =>
      __applySpecWithArity(spec, arity, __filterUndefined(...cache, ...args))

  // handle spec as Array
  if (_isArray(spec)) {
    const ret = []
    let i = 0
    const l = spec.length
    for (; i < l; i++) {
      // handle recursive spec inside array
      if (typeof spec[i] === 'object' || _isArray(spec[i])) {
        ret[i] = __applySpecWithArity(spec[i], arity, cache)
      }
      // apply spec to the key
      if (typeof spec[i] === 'function') {
        ret[i] = spec[i](...cache)
      }
    }

    return ret
  }

  // handle spec as Object
  const ret = {}
  // apply callbacks to each property in the spec object
  for (const key in spec) {
    if (spec.hasOwnProperty(key) === false || key === 'constructor') continue

    // apply the spec recursively
    if (typeof spec[key] === 'object') {
      ret[key] = __applySpecWithArity(spec[key], arity, cache)
      continue
    }

    // apply spec to the key
    if (typeof spec[key] === 'function') {
      ret[key] = spec[key](...cache)
    }
  }

  return ret
}

export function applySpec(spec, ...args) {
  // get the highest arity spec function, cache the result and pass to __applySpecWithArity
  const arity = __findHighestArity(spec)

  if (arity === 0) {
    return () => ({})
  }
  const toReturn = __applySpecWithArity(spec, arity, args)

  return toReturn
}

Tests

import {applySpec as applySpecRamda, nAry} from 'ramda'
import {add, always, compose, dec, inc, map, path, prop, T} from '../rambda'
import {applySpec} from './applySpec'

test('different than Ramda when bad spec', () => {
  const result = applySpec({sum: {a: 1}})(1, 2)
  const ramdaResult = applySpecRamda({sum: {a: 1}})(1, 2)
  expect(result).toEqual({})
  expect(ramdaResult).toEqual({sum: {a: {}}})
})

test('works with empty spec', () => {
  expect(applySpec({})()).toEqual({})
  expect(applySpec([])(1, 2)).toEqual({})
  expect(applySpec(null)(1, 2)).toEqual({})
})

test('works with unary functions', () => {
  const result = applySpec({
    v: inc,
    u: dec,
  })(1)
  const expected = {
    v: 2,
    u: 0,
  }
  expect(result).toEqual(expected)
})

test('works with binary functions', () => {
  const result = applySpec({sum: add})(1, 2)
  expect(result).toEqual({sum: 3})
})

test('works with nested specs', () => {
  const result = applySpec({
    unnested: always(0),
    nested: {sum: add},
  })(1, 2)
  const expected = {
    unnested: 0,
    nested: {sum: 3},
  }
  expect(result).toEqual(expected)
})

test('works with arrays of nested specs', () => {
  const result = applySpec({
    unnested: always(0),
    nested: [{sum: add}],
  })(1, 2)

  expect(result).toEqual({
    unnested: 0,
    nested: [{sum: 3}],
  })
})

test('works with arrays of spec objects', () => {
  const result = applySpec([{sum: add}])(1, 2)

  expect(result).toEqual([{sum: 3}])
})

test('works with arrays of functions', () => {
  const result = applySpec([map(prop('a')), map(prop('b'))])([
    {
      a: 'a1',
      b: 'b1',
    },
    {
      a: 'a2',
      b: 'b2',
    },
  ])
  const expected = [
    ['a1', 'a2'],
    ['b1', 'b2'],
  ]
  expect(result).toEqual(expected)
})

test('works with a spec defining a map key', () => {
  expect(applySpec({map: prop('a')})({a: 1})).toEqual({map: 1})
})

test('cannot retains the highest arity', () => {
  const f = applySpec({
    f1: nAry(2, T),
    f2: nAry(5, T),
  })
  const fRamda = applySpecRamda({
    f1: nAry(2, T),
    f2: nAry(5, T),
  })
  expect(f.length).toBe(0)
  expect(fRamda.length).toBe(5)
})

test('returns a curried function', () => {
  expect(applySpec({sum: add})(1)(2)).toEqual({sum: 3})
})

// Additional tests
// ============================================
test('arity', () => {
  const spec = {
    one: x1 => x1,
    two: (x1, x2) => x1 + x2,
    three: (x1, x2, x3) => x1 + x2 + x3,
  }
  expect(applySpec(spec, 1, 2, 3)).toEqual({
    one: 1,
    two: 3,
    three: 6,
  })
})

test('arity over 5 arguments', () => {
  const spec = {
    one: x1 => x1,
    two: (x1, x2) => x1 + x2,
    three: (x1, x2, x3) => x1 + x2 + x3,
    four: (x1, x2, x3, x4) => x1 + x2 + x3 + x4,
    five: (x1, x2, x3, x4, x5) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(spec, 1, 2, 3, 4, 5)).toEqual({
    one: 1,
    two: 3,
    three: 6,
    four: 10,
    five: 15,
  })
})

test('curried', () => {
  const spec = {
    one: x1 => x1,
    two: (x1, x2) => x1 + x2,
    three: (x1, x2, x3) => x1 + x2 + x3,
  }
  expect(applySpec(spec)(1)(2)(3)).toEqual({
    one: 1,
    two: 3,
    three: 6,
  })
})

test('curried over 5 arguments', () => {
  const spec = {
    one: x1 => x1,
    two: (x1, x2) => x1 + x2,
    three: (x1, x2, x3) => x1 + x2 + x3,
    four: (x1, x2, x3, x4) => x1 + x2 + x3 + x4,
    five: (x1, x2, x3, x4, x5) => x1 + x2 + x3 + x4 + x5,
  }
  expect(applySpec(spec)(1)(2)(3)(4)(5)).toEqual({
    one: 1,
    two: 3,
    three: 6,
    four: 10,
    five: 15,
  })
})

test('undefined property', () => {
  const spec = {prop: path(['property', 'doesnt', 'exist'])}
  expect(applySpec(spec, {})).toEqual({prop: undefined})
})

test('restructure json object', () => {
  const spec = {
    id: path('user.id'),
    name: path('user.firstname'),
    profile: path('user.profile'),
    doesntExist: path('user.profile.doesntExist'),
    info: {views: compose(inc, prop('views'))},
    type: always('playa'),
  }

  const data = {
    user: {
      id: 1337,
      firstname: 'john',
      lastname: 'shaft',
      profile: 'shaft69',
    },
    views: 42,
  }

  expect(applySpec(spec, data)).toEqual({
    id: 1337,
    name: 'john',
    profile: 'shaft69',
    doesntExist: undefined,
    info: {views: 43},
    type: 'playa',
  })
})

Typescript test

import {multiply, applySpec, inc, dec, add} from 'rambda'

describe('applySpec', () => {
  it('ramda 1', () => {
    const result = applySpec({
      v: inc,
      u: dec,
    })(1)
    result // $ExpectType { v: number; u: number; }
  })
  it('ramda 1', () => {
    interface Output {
      sum: number
      multiplied: number
    }
    const result = applySpec<Output>({
      sum: add,
      multiplied: multiply,
    })(1, 2)

    result // $ExpectType Output
  })
})

Rambda is faster than Ramda with 80.43%

const R = require('../../dist/rambda.js')

const curryN = [
  {
    label: 'Rambda',
    fn: () => {
      const data = {
        a: {
          b: {c: 1},
          d: 2,
        },
      }
      const spec = {
        c: R.path(['a', 'b', 'c']),
        d: R.path(['a', 'd']),
      }
      R.applySpec(spec, data)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      const data = {
        a: {
          b: {c: 1},
          d: 2,
        },
      }
      const spec = {
        c: Ramda.path(['a', 'b', 'c']),
        d: Ramda.path(['a', 'd']),
      }
      Ramda.applySpec(spec, data)
    },
  },
]

assoc

assoc<T, U, K extends string>(prop: K, val: T, obj: U): Record<K, T> & Omit<U, K>

It makes a shallow clone of obj with setting or overriding the property prop with newValue.

💥 This copies and flattens prototype properties onto the new object as well. All non-primitive properties are copied by reference.

R.assoc('c', 3, {a: 1, b: 2})
// => {a: 1, b: 2, c: 3}

Try this R.assoc example in Rambda REPL

All Typescript definitions

assoc<T, U, K extends string>(prop: K, val: T, obj: U): Record<K, T> & Omit<U, K>;
assoc<T, K extends string>(prop: K, val: T): <U>(obj: U) => Record<K, T> & Omit<U, K>;
assoc<K extends string>(prop: K): AssocPartialOne<K>;

R.assoc source

import {curry} from './curry'

function assocFn(prop, newValue, obj) {
  return Object.assign({}, obj, {[prop]: newValue})
}

export const assoc = curry(assocFn)

Tests

import {assoc} from './assoc'

test('adds a key to an empty object', () => {
  expect(assoc('a', 1, {})).toEqual({a: 1})
})

test('adds a key to a non-empty object', () => {
  expect(assoc('b', 2, {a: 1})).toEqual({
    a: 1,
    b: 2,
  })
})

test('adds a key to a non-empty object - curry case 1', () => {
  expect(assoc('b', 2)({a: 1})).toEqual({
    a: 1,
    b: 2,
  })
})

test('adds a key to a non-empty object - curry case 2', () => {
  expect(assoc('b')(2, {a: 1})).toEqual({
    a: 1,
    b: 2,
  })
})

test('adds a key to a non-empty object - curry case 3', () => {
  const result = assoc('b')(2)({a: 1})

  expect(result).toEqual({
    a: 1,
    b: 2,
  })
})

test('changes an existing key', () => {
  expect(assoc('a', 2, {a: 1})).toEqual({a: 2})
})

test('undefined is considered an empty object', () => {
  expect(assoc('a', 1, undefined)).toEqual({a: 1})
})

test('null is considered an empty object', () => {
  expect(assoc('a', 1, null)).toEqual({a: 1})
})

test('value can be null', () => {
  expect(assoc('a', null, null)).toEqual({a: null})
})

test('value can be undefined', () => {
  expect(assoc('a', undefined, null)).toEqual({a: undefined})
})

test('assignment is shallow', () => {
  expect(assoc('a', {b: 2}, {a: {c: 3}})).toEqual({a: {b: 2}})
})

Typescript test

import {assoc} from 'rambda'

const obj = {a: 1}
const newValue = 2
const newProp = 'b'

describe('R.assoc', () => {
  it('happy', () => {
    const result = assoc(newProp, newValue, obj)

    result.a // $ExpectType number
    result.b // $ExpectType number
  })
  it('curried 1', () => {
    const result = assoc(newProp, newValue)(obj)

    result.a // $ExpectType number
    result.b // $ExpectType number
  })
  it('curried 2', () => {
    const result = assoc(newProp)(newValue)(obj)

    result.a // $ExpectType number
    result.b // $ExpectType number
  })
})

Lodash is fastest. Rambda is 72.32% slower and Ramda is 60.08% slower

const R = require('../../dist/rambda.js')

const input = {
  a: 1,
  b: 2,
}
const key = 'c'
const value = 3

const assoc = [
  {
    label: 'Rambda',
    fn: () => {
      R.assoc(key, value, input)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.assoc(key, value, input)
    },
  },
  {
    label: 'Lodash.set',
    fn: () => {
      _.set(input, key, value)
    },
  },
]

assocPath

assocPath<Output>(path: Path, newValue: any, obj: object): Output

It makes a shallow clone of obj with setting or overriding with newValue the property found with path.

const path = 'b.c'
const newValue = 2
const obj = { a: 1 }

R.assocPath(path, newValue, obj)
// => { a : 1, b : { c : 2 }}

Try this R.assocPath example in Rambda REPL

All Typescript definitions

assocPath<Output>(path: Path, newValue: any, obj: object): Output;
assocPath<Output>(path: Path, newValue: any): (obj: object) => Output;
assocPath<Output>(path: Path): (newValue: any) => (obj: object) => Output;

R.assocPath source

import {_isArray} from './_internals/_isArray'
import {_isInteger} from './_internals/_isInteger'
import {assoc} from './assoc'
import {curry} from './curry'
import {cloneList} from './_internals/cloneList'

function assocPathFn(path, newValue, input) {
  const pathArrValue =
    typeof path === 'string'
      ? path.split('.').map(x => (_isInteger(Number(x)) ? Number(x) : x))
      : path
  if (pathArrValue.length === 0) {
    return newValue
  }

  const index = pathArrValue[0]
  if (pathArrValue.length > 1) {
    const condition =
      typeof input !== 'object' ||
      input === null ||
      !input.hasOwnProperty(index)

    const nextinput = condition
      ? _isInteger(pathArrValue[1])
        ? []
        : {}
      : input[index]

    newValue = assocPathFn(
      Array.prototype.slice.call(pathArrValue, 1),
      newValue,
      nextinput
    )
  }

  if (_isInteger(index) && _isArray(input)) {
    const arr = cloneList(input)
    arr[index] = newValue

    return arr
  }

  return assoc(index, newValue, input)
}

export const assocPath = curry(assocPathFn)

Tests

import {assocPath} from './assocPath'

test('string can be used as path input', () => {
  const testObj = {
    a: [{b: 1}, {b: 2}],
    d: 3,
  }
  const result = assocPath('a.0.b', 10, testObj)
  const expected = {
    a: [{b: 10}, {b: 2}],
    d: 3,
  }
  expect(result).toEqual(expected)
})

test('bug', () => {
  /*
    https://github.com/selfrefactor/rambda/issues/524
  */
  const state = {}

  const withDateLike = assocPath(
    ['outerProp', '2020-03-10'],
    {prop: 2},
    state
  )
  const withNumber = assocPath(['outerProp', '5'], {prop: 2}, state)

  const withDateLikeExpected = {outerProp: {'2020-03-10': {prop: 2}}}
  const withNumberExpected = {outerProp: {5: {prop: 2}}}
  expect(withDateLike).toEqual(withDateLikeExpected)
  expect(withNumber).toEqual(withNumberExpected)
})

test('adds a key to an empty object', () => {
  expect(assocPath(['a'], 1, {})).toEqual({a: 1})
})

test('adds a key to a non-empty object', () => {
  expect(assocPath('b', 2, {a: 1})).toEqual({
    a: 1,
    b: 2,
  })
})

test('adds a nested key to a non-empty object', () => {
  expect(assocPath('b.c', 2, {a: 1})).toEqual({
    a: 1,
    b: {c: 2},
  })
})

test('adds a nested key to a nested non-empty object - curry case 1', () => {
  expect(
    assocPath(
      'b.d',
      3
    )({
      a: 1,
      b: {c: 2},
    })
  ).toEqual({
    a: 1,
    b: {
      c: 2,
      d: 3,
    },
  })
})

test('adds a key to a non-empty object - curry case 1', () => {
  expect(assocPath('b', 2)({a: 1})).toEqual({
    a: 1,
    b: 2,
  })
})

test('adds a nested key to a non-empty object - curry case 1', () => {
  expect(assocPath('b.c', 2)({a: 1})).toEqual({
    a: 1,
    b: {c: 2},
  })
})

test('adds a key to a non-empty object - curry case 2', () => {
  expect(assocPath('b')(2, {a: 1})).toEqual({
    a: 1,
    b: 2,
  })
})

test('adds a key to a non-empty object - curry case 3', () => {
  const result = assocPath('b')(2)({a: 1})

  expect(result).toEqual({
    a: 1,
    b: 2,
  })
})

test('changes an existing key', () => {
  expect(assocPath('a', 2, {a: 1})).toEqual({a: 2})
})

test('undefined is considered an empty object', () => {
  expect(assocPath('a', 1, undefined)).toEqual({a: 1})
})

test('null is considered an empty object', () => {
  expect(assocPath('a', 1, null)).toEqual({a: 1})
})

test('value can be null', () => {
  expect(assocPath('a', null, null)).toEqual({a: null})
})

test('value can be undefined', () => {
  expect(assocPath('a', undefined, null)).toEqual({a: undefined})
})

test('assignment is shallow', () => {
  expect(assocPath('a', {b: 2}, {a: {c: 3}})).toEqual({a: {b: 2}})
})

test('empty array as path', () => {
  const result = assocPath([], 3, {
    a: 1,
    b: 2,
  })
  expect(result).toEqual(3)
})

test('happy', () => {
  const expected = {foo: {bar: {baz: 42}}}
  const result = assocPath(['foo', 'bar', 'baz'], 42, {foo: null})
  expect(result).toEqual(expected)
})

Typescript test

import {assocPath} from 'rambda'

interface Output {
  a: number
  foo: {bar: number}
}

describe('R.assocPath - user must explicitly set type of output', () => {
  it('with array as path input', () => {
    const result = assocPath<Output>(['foo', 'bar'], 2, {a: 1})

    result // $ExpectType Output
  })
  it('with string as path input', () => {
    const result = assocPath<Output>('foo.bar', 2, {a: 1})

    result // $ExpectType Output
  })
})

describe('R.assocPath - curried', () => {
  it('with array as path input', () => {
    const result = assocPath<Output>(['foo', 'bar'], 2)({a: 1})

    result // $ExpectType Output
  })
  it('with string as path input', () => {
    const result = assocPath<Output>('foo.bar', 2)({a: 1})

    result // $ExpectType Output
  })
})

bind

bind<F extends (...args: any[]) => any, T>(fn: F, thisObj: T): (...args: Parameters<F>) => ReturnType<F>

Creates a function that is bound to a context.

💥 R.bind does not provide the additional argument-binding capabilities of Function.prototype.bind.

const log = R.bind(console.log, console)
const result = R.pipe(
  R.assoc('a', 2), 
  R.tap(log), 
  R.assoc('a', 3)
)({a: 1}); 
// => result - `{a: 3}`
// => console log - `{a: 2}`

Try this R.bind example in Rambda REPL

All Typescript definitions

bind<F extends (...args: any[]) => any, T>(fn: F, thisObj: T): (...args: Parameters<F>) => ReturnType<F>;
bind<F extends (...args: any[]) => any, T>(fn: F): (thisObj: T) => (...args: Parameters<F>) => ReturnType<F>;

R.bind source

import {curryN} from './curryN'

export function bind(fn, thisObj) {
  if (arguments.length === 1) {
    return _thisObj => bind(fn, _thisObj)
  }

  return curryN(fn.length, (...args) => fn.apply(thisObj, args))
}

Tests

import {bind} from './bind'

function Foo(x) {
  this.x = x
}
function add(x) {
  return this.x + x
}
function Bar(x, y) {
  this.x = x
  this.y = y
}
Bar.prototype = new Foo()
Bar.prototype.getX = function () {
  return 'prototype getX'
}

test('returns a function', function () {
  expect(typeof bind(add)(Foo)).toEqual('function')
})

test('returns a function bound to the specified context object', function () {
  const f = new Foo(12)
  function isFoo() {
    return this instanceof Foo
  }
  const isFooBound = bind(isFoo, f)
  expect(isFoo()).toEqual(false)
  expect(isFooBound()).toEqual(true)
})

test('works with built-in types', function () {
  const abc = bind(String.prototype.toLowerCase, 'ABCDEFG')
  expect(typeof abc).toEqual('function')
  expect(abc()).toEqual('abcdefg')
})

test('works with user-defined types', function () {
  const f = new Foo(12)
  function getX() {
    return this.x
  }
  const getXFooBound = bind(getX, f)
  expect(getXFooBound()).toEqual(12)
})

test('works with plain objects', function () {
  const pojso = {
    x: 100,
  }
  function incThis() {
    return this.x + 1
  }
  const incPojso = bind(incThis, pojso)
  expect(typeof incPojso).toEqual('function')
  expect(incPojso()).toEqual(101)
})

test('does not interfere with existing object methods', function () {
  const b = new Bar('a', 'b')
  function getX() {
    return this.x
  }
  const getXBarBound = bind(getX, b)
  expect(b.getX()).toEqual('prototype getX')
  expect(getXBarBound()).toEqual('a')
})

test('preserves arity', function () {
  const f0 = function () {
    return 0
  }
  const f1 = function (a) {
    return a
  }
  const f2 = function (a, b) {
    return a + b
  }
  const f3 = function (a, b, c) {
    return a + b + c
  }

  expect(bind(f0, {}).length).toEqual(0)
  expect(bind(f1, {}).length).toEqual(1)
  expect(bind(f2, {}).length).toEqual(2)
  expect(bind(f3, {}).length).toEqual(3)
})

Typescript test

import {bind} from 'rambda'

class Foo {}
function isFoo<T = any>(this: T): boolean {
  return this instanceof Foo
}

describe('R.bind', () => {
  it('happy', () => {
    const foo = new Foo()
    const result = bind(isFoo, foo)()

    result // $ExpectType boolean
  })
})

both

both(pred1: Pred, pred2: Pred): Pred

It returns a function with input argument.

This function will return true, if both firstCondition and secondCondition return true when input is passed as their argument.

const firstCondition = x => x > 10
const secondCondition = x => x < 20
const fn = R.both(secondCondition)

const result = [fn(15), fn(30)]
// => [true, false]

Try this R.both example in Rambda REPL

All Typescript definitions

both(pred1: Pred, pred2: Pred): Pred;
both<T>(pred1: Predicate<T>, pred2: Predicate<T>): Predicate<T>;
both<T>(pred1: Predicate<T>): (pred2: Predicate<T>) => Predicate<T>;
both(pred1: Pred): (pred2: Pred) => Pred;

R.both source

export function both(f, g) {
  if (arguments.length === 1) return _g => both(f, _g)

  return (...input) => f(...input) && g(...input)
}

Tests

import {both} from './both'

const firstFn = val => val > 0
const secondFn = val => val < 10

test('with curry', () => {
  expect(both(firstFn)(secondFn)(17)).toBeFalse()
})

test('without curry', () => {
  expect(both(firstFn, secondFn)(7)).toBeTrue()
})

test('with multiple inputs', () => {
  const between = function (a, b, c) {
    return a < b && b < c
  }
  const total20 = function (a, b, c) {
    return a + b + c === 20
  }
  const fn = both(between, total20)
  expect(fn(5, 7, 8)).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function () {
    return false
  }
  const Z = function () {
    effect = 'Z got evaluated'
  }
  both(F, Z)()

  expect(effect).toBe('not evaluated')
})

Typescript test

import {both} from 'rambda'

describe('R.both', () => {
  it('with passed type', () => {
    const fn = both<number>(
      x => x > 1,
      x => x % 2 === 0
    )
    fn // $ExpectType Predicate<number>
    const result = fn(2) // $ExpectType boolean
    result // $ExpectType boolean
  })
  it('with passed type - curried', () => {
    const fn = both<number>(x => x > 1)(x => x % 2 === 0)
    fn // $ExpectType Predicate<number>
    const result = fn(2)
    result // $ExpectType boolean
  })
  it('no type passed', () => {
    const fn = both(
      x => {
        x // $ExpectType any
        return x > 1
      },
      x => {
        x // $ExpectType any
        return x % 2 === 0
      }
    )
    const result = fn(2)
    result // $ExpectType boolean
  })
  it('no type passed - curried', () => {
    const fn = both((x: number) => {
      x // $ExpectType number
      return x > 1
    })((x: number) => {
      x // $ExpectType number
      return x % 2 === 0
    })
    const result = fn(2)
    result // $ExpectType boolean
  })
})

chain

chain<T, U>(fn: (n: T) => U[], list: T[]): U[]

The method is also known as flatMap.

const duplicate = n => [ n, n ]
const list = [ 1, 2, 3 ]

const result = chain(duplicate, list)
// => [ 1, 1, 2, 2, 3, 3 ]

Try this R.chain example in Rambda REPL

All Typescript definitions

chain<T, U>(fn: (n: T) => U[], list: T[]): U[];
chain<T, U>(fn: (n: T) => U[]): (list: T[]) => U[];

R.chain source

export function chain(fn, list) {
  if (arguments.length === 1) {
    return _list => chain(fn, _list)
  }

  return [].concat(...list.map(fn))
}

Tests

import {chain} from './chain'
import {chain as chainRamda} from 'ramda'

const duplicate = n => [n, n]

test('happy', () => {
  const fn = x => [x * 2]
  const list = [1, 2, 3]

  const result = chain(fn, list)

  expect(result).toEqual([2, 4, 6])
})

test('maps then flattens one level', () => {
  expect(chain(duplicate, [1, 2, 3])).toEqual([1, 1, 2, 2, 3, 3])
})

test('maps then flattens one level - curry', () => {
  expect(chain(duplicate)([1, 2, 3])).toEqual([1, 1, 2, 2, 3, 3])
})

test('flattens only one level', () => {
  const nest = n => [[n]]
  expect(chain(nest, [1, 2, 3])).toEqual([[1], [2], [3]])
})

test('can compose', () => {
  function dec(x) {
    return [x - 1]
  }
  function times2(x) {
    return [x * 2]
  }

  var mdouble = chain(times2)
  var mdec = chain(dec)
  expect(mdec(mdouble([10, 20, 30]))).toEqual([19, 39, 59])
})

test('@types/ramda broken test', () => {
  const score = {
    maths: 90,
    physics: 80,
  }

  const calculateTotal = score => {
    const {maths, physics} = score
    return maths + physics
  }

  const assocTotalToScore = (total, score) => ({...score, total})

  const calculateAndAssocTotalToScore = chainRamda(
    assocTotalToScore,
    calculateTotal
  )
  expect(() => calculateAndAssocTotalToScore(score)).toThrow()
})

Typescript test

import {chain} from 'rambda'

const list = [1, 2, 3]
const fn = (x: number) => [`${x}`, `${x}`]

describe('R.chain', () => {
  it('without passing type', () => {
    const result = chain(fn, list)
    result // $ExpectType string[]

    const curriedResult = chain(fn)(list)
    curriedResult // $ExpectType string[]
  })
})

clamp

Restrict a number input to be within min and max limits.

If input is bigger than max, then the result is max.

If input is smaller than min, then the result is min.

const result = [
  R.clamp(0, 10, 5), 
  R.clamp(0, 10, -1),
  R.clamp(0, 10, 11)
]
// => [5, 0, 10]

Try this R.clamp example in Rambda REPL

clone

It creates a deep copy of the input, which may contain (nested) Arrays and Objects, Numbers, Strings, Booleans and Dates.

const objects = [{a: 1}, {b: 2}];
const objectsClone = R.clone(objects);

const result = [
  R.equals(objects, objectsClone),
  R.equals(objects[0], objectsClone[0]),
] // => [ true, true ]

Try this R.clone example in Rambda REPL

complement

It returns inverted version of origin function that accept input as argument.

The return value of inverted is the negative boolean value of origin(input).

const origin = x => x > 5
const inverted = complement(origin)

const result = [
  origin(7),
  inverted(7)
] => [ true, false ]

Try this R.complement example in Rambda REPL

compose

It performs right-to-left function composition.

const result = R.compose(
  R.map(x => x * 2),
  R.filter(x => x > 2)
)([1, 2, 3, 4])

// => [6, 8]

Try this R.compose example in Rambda REPL

concat

It returns a new string or array, which is the result of merging x and y.

R.concat([1, 2])([3, 4]) // => [1, 2, 3, 4]
R.concat('foo', 'bar') // => 'foobar'

Try this R.concat example in Rambda REPL

cond

It takes list with conditions and returns a new function fn that expects input as argument.

This function will start evaluating the conditions in order to find the first winner(order of conditions matter).

The winner is this condition, which left side returns true when input is its argument. Then the evaluation of the right side of the winner will be the final result.

If no winner is found, then fn returns undefined.

const fn = R.cond([
  [ x => x > 25, R.always('more than 25') ],
  [ x => x > 15, R.always('more than 15') ],
  [ R.T, x => `${x} is nothing special` ],
])

const result = [
  fn(30),
  fn(20),
  fn(10),
] 
// => ['more than 25', 'more than 15', '10 is nothing special']

Try this R.cond example in Rambda REPL

converge

Accepts a converging function and a list of branching functions and returns a new function. When invoked, this new function is applied to some arguments, each branching function is applied to those same arguments. The results of each branching function are passed as arguments to the converging function to produce the return value.

💥 Explanation is taken from Ramda documentation

const result = R.converge(R.multiply)([ R.add(1), R.add(3) ])(2)
// => 15

Try this R.converge example in Rambda REPL

curry

It expects a function as input and returns its curried version.

const fn = (a, b, c) => a + b + c
const curried = R.curry(fn)
const sum = curried(1,2)

const result = sum(3) // => 6

Try this R.curry example in Rambda REPL

curryN

It returns a curried equivalent of the provided function, with the specified arity.

dec

It decrements a number.

defaultTo

defaultTo<T>(defaultValue: T, input: T | null | undefined): T

It returns defaultValue, if all of inputArguments are undefined, null or NaN.

Else, it returns the first truthy inputArguments instance(from left to right).

💥 Rambda's defaultTo accept indefinite number of arguments when non curried, i.e. R.defaultTo(2, foo, bar, baz).

R.defaultTo('foo', 'bar') // => 'bar'
R.defaultTo('foo', undefined) // => 'foo'

// Important - emtpy string is not falsy value(same as Ramda)
R.defaultTo('foo', '') // => 'foo'

Try this R.defaultTo example in Rambda REPL

All Typescript definitions

defaultTo<T>(defaultValue: T, input: T | null | undefined): T;
defaultTo<T>(defaultValue: T): (input: T | null | undefined) => T;

R.defaultTo source

function isFalsy(input) {
  return (
    input === undefined || input === null || Number.isNaN(input) === true
  )
}

export function defaultTo(defaultArgument, input) {
  if (arguments.length === 1) {
    return _input => defaultTo(defaultArgument, _input)
  }

  return isFalsy(input) ? defaultArgument : input
}

Tests

import {defaultTo} from './defaultTo'

test('with undefined', () => {
  expect(defaultTo('foo')(undefined)).toEqual('foo')
})

test('with null', () => {
  expect(defaultTo('foo')(null)).toEqual('foo')
})

test('with NaN', () => {
  expect(defaultTo('foo')(NaN)).toEqual('foo')
})

test('with empty string', () => {
  expect(defaultTo('foo', '')).toEqual('')
})

test('with false', () => {
  expect(defaultTo('foo', false)).toEqual(false)
})

test('when inputArgument passes initial check', () => {
  expect(defaultTo('foo', 'bar')).toEqual('bar')
})

Typescript test

import {defaultTo} from 'rambda'

describe('R.defaultTo with Ramda spec', () => {
  it('happy', () => {
    const result = defaultTo('foo', '')
    result // $ExpectType "" | "foo"
  })
  it('with explicit type', () => {
    const result = defaultTo<string>('foo', null)
    result // $ExpectType string
  })
})

Rambda is faster than Ramda with 48.91%

const R = require('../../dist/rambda.js')

const input = [null, undefined, 5]

const defaultTo = [
  {
    label: 'Rambda',
    fn: () => {
      R.defaultTo(3, input[0])
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.defaultTo(3, input[0])
    },
  },
  {
    label: 'Rambda with multiple arguments',
    fn: () => {
      R.defaultTo(3, ...input)
    },
  },
]

difference

difference<T>(a: T[], b: T[]): T[]

It returns the uniq set of all elements in the first list a not contained in the second list b.

R.equals is used to determine equality.

const a = [ 1, 2, 3, 4 ]
const b = [ 3, 4, 5, 6 ]

const result = difference(a, b)
// => [ 1, 2 ]

Try this R.difference example in Rambda REPL

All Typescript definitions

difference<T>(a: T[], b: T[]): T[];
difference<T>(a: T[]): (b: T[]) => T[];

R.difference source

import {includes} from './includes'
import {uniq} from './uniq'

export function difference(a, b) {
  if (arguments.length === 1) return _b => difference(a, _b)

  return uniq(a).filter(aInstance => !includes(aInstance, b))
}

Tests

import {difference} from './difference'
import {difference as differenceRamda} from 'ramda'

test('difference', () => {
  const a = [1, 2, 3, 4]
  const b = [3, 4, 5, 6]
  expect(difference(a)(b)).toEqual([1, 2])

  expect(difference([], [])).toEqual([])
})

test('difference with objects', () => {
  const a = [{id: 1}, {id: 2}, {id: 3}, {id: 4}]
  const b = [{id: 3}, {id: 4}, {id: 5}, {id: 6}]
  expect(difference(a, b)).toEqual([{id: 1}, {id: 2}])
})

test('no duplicates in first list', () => {
  const M2 = [1, 2, 3, 4, 1, 2, 3, 4]
  const N2 = [3, 3, 4, 4, 5, 5, 6, 6]
  expect(difference(M2, N2)).toEqual([1, 2])
})

test('should use R.equals', () => {
  expect(difference([1], [1]).length).toEqual(0)
  expect(differenceRamda([NaN], [NaN]).length).toEqual(0)
})

Typescript test

import {difference} from 'rambda'

const list1 = [1, 2, 3]
const list2 = [1, 2, 4]

describe('R.difference', () => {
  it('happy', () => {
    const result = difference(list1, list2)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = difference(list1)(list2)

    result // $ExpectType number[]
  })
})

dissoc

It returns a new object that does not contain property prop.

R.dissoc('b', {a: 1, b: 2, c: 3})
// => {a: 1, c: 3}

Try this R.dissoc example in Rambda REPL

divide

R.divide(71, 100) // => 0.71

Try this R.divide example in Rambda REPL

drop

drop<T>(howMany: number, input: T[]): T[]

It returns howMany items dropped from beginning of list or string input.

R.drop(2, ['foo', 'bar', 'baz']) // => ['baz']
R.drop(2, 'foobar')  // => 'obar'

Try this R.drop example in Rambda REPL

All Typescript definitions

drop<T>(howMany: number, input: T[]): T[];
drop(howMany: number, input: string): string;
drop<T>(howMany: number): {
  <T>(input: T[]): T[];
  (input: string): string;
};

R.drop source

export function drop(howManyToDrop, listOrString) {
  if (arguments.length === 1) return _list => drop(howManyToDrop, _list)

  return listOrString.slice(howManyToDrop > 0 ? howManyToDrop : 0)
}

Tests

import assert from 'assert'

import {drop} from './drop'

test('with array', () => {
  expect(drop(2)(['foo', 'bar', 'baz'])).toEqual(['baz'])
  expect(drop(3, ['foo', 'bar', 'baz'])).toEqual([])
  expect(drop(4, ['foo', 'bar', 'baz'])).toEqual([])
})

test('with string', () => {
  expect(drop(3, 'rambda')).toEqual('bda')
})

test('with non-positive count', () => {
  expect(drop(0, [1, 2, 3])).toEqual([1, 2, 3])
  expect(drop(-1, [1, 2, 3])).toEqual([1, 2, 3])
  expect(drop(-Infinity, [1, 2, 3])).toEqual([1, 2, 3])
})

test('should return copy', () => {
  const xs = [1, 2, 3]

  assert.notStrictEqual(drop(0, xs), xs)
  assert.notStrictEqual(drop(-1, xs), xs)
})

Typescript test

import {drop} from 'rambda'

const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2

describe('R.drop - array', () => {
  it('happy', () => {
    const result = drop(howMany, list)
    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = drop(howMany)(list)
    result // $ExpectType number[]
  })
})

describe('R.drop - string', () => {
  it('happy', () => {
    const result = drop(howMany, str)
    result // $ExpectType string
  })
  it('curried', () => {
    const result = drop(howMany)(str)
    result // $ExpectType string
  })
})

Rambda is faster than Ramda with 82.35%

const R = require('../../dist/rambda.js')

const input = [1, 2, 3, 4]

const drop = [
  {
    label: 'Rambda',
    fn: () => {
      R.drop(3, input)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.drop(3, input)
    },
  },
]

dropLast

dropLast<T>(howMany: number, input: T[]): T[]

It returns howMany items dropped from the end of list or string input.

R.dropLast(2, ['foo', 'bar', 'baz']) // => ['foo']
R.dropLast(2, 'foobar')  // => 'foob'

Try this R.dropLast example in Rambda REPL

All Typescript definitions

dropLast<T>(howMany: number, input: T[]): T[];
dropLast(howMany: number, input: string): string;
dropLast<T>(howMany: number): {
  <T>(input: T[]): T[];
  (input: string): string;
};

R.dropLast source

export function dropLast(howManyToDrop, listOrString) {
  if (arguments.length === 1) {
    return _listOrString => dropLast(howManyToDrop, _listOrString)
  }

  return howManyToDrop > 0
    ? listOrString.slice(0, -howManyToDrop)
    : listOrString.slice()
}

Tests

import assert from 'assert'

import {dropLast} from './dropLast'

test('with array', () => {
  expect(dropLast(2)(['foo', 'bar', 'baz'])).toEqual(['foo'])
  expect(dropLast(3, ['foo', 'bar', 'baz'])).toEqual([])
  expect(dropLast(4, ['foo', 'bar', 'baz'])).toEqual([])
})

test('with string', () => {
  expect(dropLast(3, 'rambda')).toEqual('ram')
})

test('with non-positive count', () => {
  expect(dropLast(0, [1, 2, 3])).toEqual([1, 2, 3])
  expect(dropLast(-1, [1, 2, 3])).toEqual([1, 2, 3])
  expect(dropLast(-Infinity, [1, 2, 3])).toEqual([1, 2, 3])
})

test('should return copy', () => {
  const xs = [1, 2, 3]

  assert.notStrictEqual(dropLast(0, xs), xs)
  assert.notStrictEqual(dropLast(-1, xs), xs)
})

Typescript test

import {dropLast} from 'rambda'

const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2

describe('R.dropLast - array', () => {
  it('happy', () => {
    const result = dropLast(howMany, list)
    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = dropLast(howMany)(list)
    result // $ExpectType number[]
  })
})

describe('R.dropLast - string', () => {
  it('happy', () => {
    const result = dropLast(howMany, str)
    result // $ExpectType string
  })
  it('curried', () => {
    const result = dropLast(howMany)(str)
    result // $ExpectType string
  })
})

Rambda is faster than Ramda with 86.74%

const R = require('../../dist/rambda.js')

const input = [1, 2, 3, 4]

const dropLast = [
  {
    label: 'Rambda',
    fn: () => {
      R.dropLast(3, input)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.dropLast(3, input)
    },
  },
]

dropLastWhile

const list = [1, 2, 3, 4, 5];
const predicate = x => x >= 3

const result = dropLastWhile(predicate, list);
// => [1, 2]

Try this R.dropLastWhile example in Rambda REPL

dropRepeats

dropRepeats<T>(list: T[]): T[]

It removes any successive duplicates according to R.equals.

const result = R.dropRepeats([
  1, 
  1, 
  {a: 1}, 
  {a:1}, 
  1
])
// => [1, {a: 1}, 1]

Try this R.dropRepeats example in Rambda REPL

All Typescript definitions

dropRepeats<T>(list: T[]): T[];

R.dropRepeats source

import {_isArray} from './_internals/_isArray'
import {equals} from './equals'

export function dropRepeats(list) {
  if (!_isArray(list)) {
    throw new Error(`${list} is not a list`)
  }

  const toReturn = []

  list.reduce((prev, current) => {
    if (!equals(prev, current)) {
      toReturn.push(current)
    }

    return current
  }, undefined)

  return toReturn
}

Tests

import {dropRepeats as dropRepeatsRamda} from 'ramda'

import {compareCombinations} from './_internals/testUtils'
import {add} from './add'
import {dropRepeats} from './dropRepeats'

const list = [1, 2, 2, 2, 3, 4, 4, 5, 5, 3, 2, 2, {a: 1}, {a: 1}]
const listClean = [1, 2, 3, 4, 5, 3, 2, {a: 1}]

test('happy', () => {
  const result = dropRepeats(list)
  expect(result).toEqual(listClean)
})

const possibleLists = [
  [add(1), async () => {}, [1], [1], [2], [2]],
  [add(1), add(1), add(2)],
  [],
  1,
  /foo/g,
  Promise.resolve(1),
]

describe('brute force', () => {
  compareCombinations({
    firstInput: possibleLists,
    callback: errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        Object {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 1,
          "SHOULD_NOT_THROW": 3,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 6,
        }
      `)
    },
    fn: dropRepeats,
    fnRamda: dropRepeatsRamda,
  })
})

Typescript test

import {dropRepeats} from 'rambda'

describe('R.dropRepeats', () => {
  it('happy', () => {
    const result = dropRepeats([1, 2, 2, 3])

    result // $ExpectType number[]
  })
})

dropRepeatsWith

const list = [{a:1,b:2}, {a:1,b:3}, {a:2, b:4}]
const result = R.dropRepeatsWith(R.prop('a'), list)

// => [{a:1,b:2}, {a:2, b:4}]

Try this R.dropRepeatsWith example in Rambda REPL

dropWhile

const list = [1, 2, 3, 4]
const predicate = x => x < 3
const result = R.dropWhile(predicate, list)
// => [3, 4]

Try this R.dropWhile example in Rambda REPL

either

either(firstPredicate: Pred, secondPredicate: Pred): Pred

It returns a new predicate function from firstPredicate and secondPredicate inputs.

This predicate function will return true, if any of the two input predicates return true.

const firstPredicate = x => x > 10
const secondPredicate = x => x % 2 === 0
const predicate = R.either(firstPredicate, secondPredicate)

const result = [
  predicate(15),
  predicate(8),
  predicate(7),
]
// => [true, true, false]

Try this R.either example in Rambda REPL

All Typescript definitions

either(firstPredicate: Pred, secondPredicate: Pred): Pred;
either<T>(firstPredicate: Predicate<T>, secondPredicate: Predicate<T>): Predicate<T>;
either<T>(firstPredicate: Predicate<T>): (secondPredicate: Predicate<T>) => Predicate<T>;
either(firstPredicate: Pred): (secondPredicate: Pred) => Pred;

R.either source

export function either(firstPredicate, secondPredicate) {
  if (arguments.length === 1) {
    return _secondPredicate => either(firstPredicate, _secondPredicate)
  }

  return (...input) =>
    Boolean(firstPredicate(...input) || secondPredicate(...input))
}

Tests

import {either} from './either'

test('with multiple inputs', () => {
  const between = function (a, b, c) {
    return a < b && b < c
  }
  const total20 = function (a, b, c) {
    return a + b + c === 20
  }
  const fn = either(between, total20)
  expect(fn(7, 8, 5)).toBeTrue()
})

test('skip evaluation of the second expression', () => {
  let effect = 'not evaluated'
  const F = function () {
    return true
  }
  const Z = function () {
    effect = 'Z got evaluated'
  }
  either(F, Z)()

  expect(effect).toBe('not evaluated')
})

test('case 1', () => {
  const firstFn = val => val > 0
  const secondFn = val => val * 5 > 10

  expect(either(firstFn, secondFn)(1)).toBeTrue()
})

test('case 2', () => {
  const firstFn = val => val > 0
  const secondFn = val => val === -10
  const fn = either(firstFn)(secondFn)

  expect(fn(-10)).toBeTrue()
})

Typescript test

import {either} from 'rambda'

describe('R.either', () => {
  it('with passed type', () => {
    const fn = either<number>(
      x => x > 1,
      x => x % 2 === 0
    )
    fn // $ExpectType Predicate<number>
    const result = fn(2) // $ExpectType boolean
    result // $ExpectType boolean
  })
  it('with passed type - curried', () => {
    const fn = either<number>(x => x > 1)(x => x % 2 === 0)
    fn // $ExpectType Predicate<number>
    const result = fn(2)
    result // $ExpectType boolean
  })
  it('no type passed', () => {
    const fn = either(
      x => {
        x // $ExpectType any
        return x > 1
      },
      x => {
        x // $ExpectType any
        return x % 2 === 0
      }
    )
    const result = fn(2)
    result // $ExpectType boolean
  })
  it('no type passed - curried', () => {
    const fn = either((x: number) => {
      x // $ExpectType number
      return x > 1
    })((x: number) => {
      x // $ExpectType number
      return x % 2 === 0
    })
    const result = fn(2)
    result // $ExpectType boolean
  })
})

endsWith

endsWith(target: string, iterable: string): boolean

When iterable is a string, then it behaves as String.prototype.endsWith. When iterable is a list, then it uses R.equals to determine if the target list ends in the same way as the given target.

const str = 'foo-bar'
const list = [{a:1}, {a:2}, {a:3}]

const result = [
  R.endsWith('bar', str),
  R.endsWith([{a:1}, {a:2}], list)
]
// => [true, true]

Try this R.endsWith example in Rambda REPL

All Typescript definitions

endsWith(target: string, iterable: string): boolean;
endsWith(target: string): (iterable: string) => boolean;
endsWith<T>(target: T[], list: T[]): boolean;
endsWith<T>(target: T[]): (list: T[]) => boolean;

R.endsWith source

import {equals} from './equals.js'
import {_isArray} from './_internals/_isArray.js'

export function endsWith(target, iterable) {
  if (arguments.length === 1) return _iterable => endsWith(target, _iterable)

  if (typeof iterable === 'string') {
    return iterable.endsWith(target)
  }
  if (!_isArray(target)) return false

  const diff = iterable.length - target.length
  let correct = true
  const filtered = target.filter((x, index) => {
    if (!correct) return false
    const result = equals(x, iterable[index + diff])
    if (!result) correct = false
    return result
  })

  return filtered.length === target.length
}

Tests

import {endsWith} from './endsWith'
import {endsWith as endsWithRamda} from 'ramda'
import {compareCombinations} from './_internals/testUtils'

test('with string', () => {
  expect(endsWith('bar', 'foo-bar')).toBeTrue()
  expect(endsWith('baz')('foo-bar')).toBeFalse()
})

test('use R.equals with array', () => {
  const list = [{a: 1}, {a: 2}, {a: 3}]
  expect(endsWith({a: 3}, list)).toBeFalse(),
    expect(endsWith([{a: 3}], list)).toBeTrue()
  expect(endsWith([{a: 2}, {a: 3}], list)).toBeTrue()
  expect(endsWith(list, list)).toBeTrue()
  expect(endsWith([{a: 1}], list)).toBeFalse()
})

export const possibleTargets = [
  NaN,
  [NaN],
  /foo/,
  [/foo/],
  Promise.resolve(1),
  [Promise.resolve(1)],
  Error('foo'),
  [Error('foo')],
]

export const possibleIterables = [
  [Promise.resolve(1), Promise.resolve(2)],
  [/foo/, /bar/],
  [NaN],
  [Error('foo'), Error('bar')],
]

describe('brute force', () => {
  compareCombinations({
    fn: endsWith,
    fnRamda: endsWithRamda,
    firstInput: possibleTargets,
    secondInput: possibleIterables,
    callback: errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        Object {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 0,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 32,
        }
      `)
    },
  })
})

Typescript test

import {endsWith} from 'rambda'

describe('R.endsWith - array as iterable', () => {
  const target = [{a: 2}]
  const iterable = [{a: 1}, {a: 2}]
  it('happy', () => {
    const result = endsWith(target, iterable)

    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = endsWith(target)(iterable)

    result // $ExpectType boolean
  })
})

describe('R.endsWith - string as iterable', () => {
  const target = 'bar'
  const iterable = 'foo bar'
  it('happy', () => {
    const result = endsWith(target, iterable)

    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = endsWith(target)(iterable)

    result // $ExpectType boolean
  })
})

eqProps

It returns true if property prop in obj1 is equal to property prop in obj2 according to R.equals.

const obj1 = {a: 1, b:2}
const obj2 = {a: 1, b:3}
const result = R.eqProps('a', obj1, obj2)
// => true

Try this R.eqProps example in Rambda REPL

equals

equals<T>(x: T, y: T): boolean

It deeply compares x and y and returns true if they are equal.

💥 It doesn't handle cyclical data structures and functions

R.equals(
  [1, {a:2}, [{b: 3}]],
  [1, {a:2}, [{b: 3}]]
) // => true

Try this R.equals example in Rambda REPL

All Typescript definitions

equals<T>(x: T, y: T): boolean;
equals<T>(x: T): (y: T) => boolean;

R.equals source

import {type} from './type'
import {_isArray} from './_internals/_isArray'

export function _lastIndexOf(valueToFind, list) {
  if (!_isArray(list)) {
    throw new Error(`Cannot read property 'indexOf' of ${list}`)
  }
  const typeOfValue = type(valueToFind)
  if (!['Object', 'Array', 'NaN', 'RegExp'].includes(typeOfValue))
    return list.lastIndexOf(valueToFind)

  const {length} = list
  let index = length
  let foundIndex = -1

  while (--index > -1 && foundIndex === -1) {
    if (equals(list[index], valueToFind)) {
      foundIndex = index
    }
  }

  return foundIndex
}

export function _indexOf(valueToFind, list) {
  if (!_isArray(list)) {
    throw new Error(`Cannot read property 'indexOf' of ${list}`)
  }
  const typeOfValue = type(valueToFind)
  if (!['Object', 'Array', 'NaN', 'RegExp'].includes(typeOfValue))
    return list.indexOf(valueToFind)

  let index = -1
  let foundIndex = -1
  const {length} = list

  while (++index < length && foundIndex === -1) {
    if (equals(list[index], valueToFind)) {
      foundIndex = index
    }
  }

  return foundIndex
}

function _arrayFromIterator(iter) {
  const list = []
  let next
  while (!(next = iter.next()).done) {
    list.push(next.value)
  }
  return list
}

function _equalsSets(a, b) {
  if (a.size !== b.size) {
    return false
  }
  const aList = _arrayFromIterator(a.values())
  const bList = _arrayFromIterator(b.values())

  const filtered = aList.filter(
    aInstance => _indexOf(aInstance, bList) === -1
  )
  return filtered.length === 0
}

function parseError(maybeError) {
  const typeofError = maybeError.__proto__.toString()
  if (!['Error', 'TypeError'].includes(typeofError)) return []

  return [typeofError, maybeError.message]
}

function parseDate(maybeDate) {
  if (!maybeDate.toDateString) return [false]

  return [true, maybeDate.getTime()]
}

function parseRegex(maybeRegex) {
  if (maybeRegex.constructor !== RegExp) return [false]

  return [true, maybeRegex.toString()]
}

function equalsSets(a, b) {
  if (a.size !== b.size) {
    return false
  }
  const aList = _arrayFromIterator(a.values())
  const bList = _arrayFromIterator(b.values())

  const filtered = aList.filter(
    aInstance => _indexOf(aInstance, bList) === -1
  )
  return filtered.length === 0
}

export function equals(a, b) {
  if (arguments.length === 1) return _b => equals(a, _b)

  const aType = type(a)

  if (aType !== type(b)) return false
  if (aType === 'Function') {
    return a.name === undefined ? false : a.name === b.name
  }

  if (['NaN', 'Undefined', 'Null'].includes(aType)) return true

  if (aType === 'Number') {
    if (Object.is(-0, a) !== Object.is(-0, b)) return false

    return a.toString() === b.toString()
  }

  if (['String', 'Boolean'].includes(aType)) {
    return a.toString() === b.toString()
  }

  if (aType === 'Array') {
    const aClone = Array.from(a)
    const bClone = Array.from(b)

    if (aClone.toString() !== bClone.toString()) {
      return false
    }

    let loopArrayFlag = true
    aClone.forEach((aCloneInstance, aCloneIndex) => {
      if (loopArrayFlag) {
        if (
          aCloneInstance !== bClone[aCloneIndex] &&
          !equals(aCloneInstance, bClone[aCloneIndex])
        ) {
          loopArrayFlag = false
        }
      }
    })

    return loopArrayFlag
  }

  const aRegex = parseRegex(a)
  const bRegex = parseRegex(b)

  if (aRegex[0]) {
    return bRegex[0] ? aRegex[1] === bRegex[1] : false
  } else if (bRegex[0]) return false

  const aDate = parseDate(a)
  const bDate = parseDate(b)

  if (aDate[0]) {
    return bDate[0] ? aDate[1] === bDate[1] : false
  } else if (bDate[0]) return false

  const aError = parseError(a)
  const bError = parseError(b)

  if (aError[0]) {
    return bError[0]
      ? aError[0] === bError[0] && aError[1] === bError[1]
      : false
  }
  if (aType === 'Set') {
    return _equalsSets(a, b)
  }
  if (aType === 'Object') {
    const aKeys = Object.keys(a)

    if (aKeys.length !== Object.keys(b).length) {
      return false
    }

    let loopObjectFlag = true
    aKeys.forEach(aKeyInstance => {
      if (loopObjectFlag) {
        const aValue = a[aKeyInstance]
        const bValue = b[aKeyInstance]

        if (aValue !== bValue && !equals(aValue, bValue)) {
          loopObjectFlag = false
        }
      }
    })

    return loopObjectFlag
  }

  return false
}

Tests

import {equals} from './equals'
import {equals as equalsRamda} from 'ramda'
import {compareCombinations} from './_internals/testUtils'
import {variousTypes} from './benchmarks/_utils'

test('compare functions', () => {
  function foo() {}
  function bar() {}
  const baz = () => {}

  const expectTrue = equals(foo, foo)
  const expectFalseFirst = equals(foo, bar)
  const expectFalseSecond = equals(foo, baz)

  expect(expectTrue).toBeTrue()
  expect(expectFalseFirst).toBeFalse()
  expect(expectFalseSecond).toBeFalse()
})

test('with array of objects', () => {
  const list1 = [{a: 1}, [{b: 2}]]
  const list2 = [{a: 1}, [{b: 2}]]
  const list3 = [{a: 1}, [{b: 3}]]

  expect(equals(list1, list2)).toBeTrue()
  expect(equals(list1, list3)).toBeFalse()
})

test('with regex', () => {
  expect(equals(/s/, /s/)).toEqual(true)
  expect(equals(/s/, /d/)).toEqual(false)
  expect(equals(/a/gi, /a/gi)).toEqual(true)
  expect(equals(/a/gim, /a/gim)).toEqual(true)
  expect(equals(/a/gi, /a/i)).toEqual(false)
})

test('not a number', () => {
  expect(equals([NaN], [NaN])).toBeTrue()
})

test('new number', () => {
  expect(equals(new Number(0), new Number(0))).toEqual(true)
  expect(equals(new Number(0), new Number(1))).toEqual(false)
  expect(equals(new Number(1), new Number(0))).toEqual(false)
})

test('new string', () => {
  expect(equals(new String(''), new String(''))).toEqual(true)
  expect(equals(new String(''), new String('x'))).toEqual(false)
  expect(equals(new String('x'), new String(''))).toEqual(false)
  expect(equals(new String('foo'), new String('foo'))).toEqual(true)
  expect(equals(new String('foo'), new String('bar'))).toEqual(false)
  expect(equals(new String('bar'), new String('foo'))).toEqual(false)
})

test('new Boolean', () => {
  expect(equals(new Boolean(true), new Boolean(true))).toEqual(true)
  expect(equals(new Boolean(false), new Boolean(false))).toEqual(true)
  expect(equals(new Boolean(true), new Boolean(false))).toEqual(false)
  expect(equals(new Boolean(false), new Boolean(true))).toEqual(false)
})

test('new Error', () => {
  expect(equals(new Error('XXX'), {})).toEqual(false)
  expect(equals(new Error('XXX'), new TypeError('XXX'))).toEqual(false)
  expect(equals(new Error('XXX'), new Error('YYY'))).toEqual(false)
  expect(equals(new Error('XXX'), new Error('XXX'))).toEqual(true)
  expect(equals(new Error('XXX'), new TypeError('YYY'))).toEqual(false)
})

test('with dates', () => {
  expect(equals(new Date(0), new Date(0))).toEqual(true)
  expect(equals(new Date(1), new Date(1))).toEqual(true)
  expect(equals(new Date(0), new Date(1))).toEqual(false)
  expect(equals(new Date(1), new Date(0))).toEqual(false)
  expect(equals(new Date(0), {})).toEqual(false)
  expect(equals({}, new Date(0))).toEqual(false)
})

test('ramda spec', () => {
  expect(equals({}, {})).toEqual(true)

  expect(
    equals(
      {
        a: 1,
        b: 2,
      },
      {
        a: 1,
        b: 2,
      }
    )
  ).toEqual(true)

  expect(
    equals(
      {
        a: 2,
        b: 3,
      },
      {
        b: 3,
        a: 2,
      }
    )
  ).toEqual(true)

  expect(
    equals(
      {
        a: 2,
        b: 3,
      },
      {
        a: 3,
        b: 3,
      }
    )
  ).toEqual(false)

  expect(
    equals(
      {
        a: 2,
        b: 3,
        c: 1,
      },
      {
        a: 2,
        b: 3,
      }
    )
  ).toEqual(false)
})

test('works with boolean tuple', () => {
  expect(equals([true, false], [true, false])).toBeTrue()
  expect(equals([true, false], [true, true])).toBeFalse()
})

test('works with equal objects within array', () => {
  const objFirst = {
    a: {
      b: 1,
      c: 2,
      d: [1],
    },
  }
  const objSecond = {
    a: {
      b: 1,
      c: 2,
      d: [1],
    },
  }

  const x = [1, 2, objFirst, null, '', []]
  const y = [1, 2, objSecond, null, '', []]
  expect(equals(x, y)).toBeTrue()
})

test('works with different objects within array', () => {
  const objFirst = {a: {b: 1}}
  const objSecond = {a: {b: 2}}

  const x = [1, 2, objFirst, null, '', []]
  const y = [1, 2, objSecond, null, '', []]
  expect(equals(x, y)).toBeFalse()
})

test('works with undefined as second argument', () => {
  expect(equals(1, undefined)).toBeFalse()

  expect(equals(undefined, undefined)).toBeTrue()
})

test('compare sets', () => {
  const toCompareDifferent = new Set([{a: 1}, {a: 2}])
  const toCompareSame = new Set([{a: 1}, {a: 2}, {a: 1}])
  const testSet = new Set([{a: 1}, {a: 2}, {a: 1}])
  expect(equals(toCompareSame, testSet)).toBeTruthy()
  expect(equals(toCompareDifferent, testSet)).toBeFalsy()
  expect(equalsRamda(toCompareSame, testSet)).toBeTruthy()
  expect(equalsRamda(toCompareDifferent, testSet)).toBeFalsy()
})

test('compare simple sets', () => {
  const testSet = new Set(['2', '3', '3', '2', '1'])
  expect(equals(new Set(['3', '2', '1']), testSet)).toBeTruthy()
  expect(equals(new Set(['3', '2', '0']), testSet)).toBeFalsy()
})

test('various examples', () => {
  expect(equals([1, 2, 3])([1, 2, 3])).toBeTrue()

  expect(equals([1, 2, 3], [1, 2])).toBeFalse()

  expect(equals(1, 1)).toBeTrue()

  expect(equals(1, '1')).toBeFalse()

  expect(equals({}, {})).toBeTrue()

  expect(
    equals(
      {
        a: 1,
        b: 2,
      },
      {
        b: 2,
        a: 1,
      }
    )
  ).toBeTrue()

  expect(
    equals(
      {
        a: 1,
        b: 2,
      },
      {
        a: 1,
        b: 1,
      }
    )
  ).toBeFalse()

  expect(
    equals(
      {
        a: 1,
        b: false,
      },
      {
        a: 1,
        b: 1,
      }
    )
  ).toBeFalse()

  expect(
    equals(
      {
        a: 1,
        b: 2,
      },
      {
        b: 2,
        a: 1,
        c: 3,
      }
    )
  ).toBeFalse()

  expect(
    equals(
      {
        x: {
          a: 1,
          b: 2,
        },
      },
      {
        x: {
          b: 2,
          a: 1,
          c: 3,
        },
      }
    )
  ).toBeFalse()

  expect(
    equals(
      {
        a: 1,
        b: 2,
      },
      {
        b: 3,
        a: 1,
      }
    )
  ).toBeFalse()

  expect(equals({a: {b: {c: 1}}}, {a: {b: {c: 1}}})).toBeTrue()

  expect(equals({a: {b: {c: 1}}}, {a: {b: {c: 2}}})).toBeFalse()

  expect(equals({a: {}}, {a: {}})).toBeTrue()

  expect(equals('', '')).toBeTrue()

  expect(equals('foo', 'foo')).toBeTrue()

  expect(equals('foo', 'bar')).toBeFalse()

  expect(equals(0, false)).toBeFalse()

  expect(equals(/\s/g, null)).toBeFalse()

  expect(equals(null, null)).toBeTrue()

  expect(equals(false)(null)).toBeFalse()
})

test('with custom functions', () => {
  function foo() {
    return 1
  }
  foo.prototype.toString = () => ''
  const result = equals(foo, foo)

  expect(result).toBeTrue()
})

test('with classes', () => {
  class Foo {}
  const foo = new Foo()
  const result = equals(foo, foo)

  expect(result).toBeTrue()
})

test('with negative zero', () => {
  expect(equals(-0, -0)).toBeTrue()
  expect(equals(-0, 0)).toBeFalse()
  expect(equals(0, 0)).toBeTrue()
  expect(equals(-0, 1)).toBeFalse()
})

const possibleInputs = variousTypes

describe('brute force', () => {
  compareCombinations({
    fn: equals,
    fnRamda: equalsRamda,
    firstInput: possibleInputs,
    secondInput: possibleInputs,
    callback: errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        Object {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 5,
          "SHOULD_NOT_THROW": 4,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 289,
        }
      `)
    },
  })
})

Typescript test

import {equals} from 'rambda'

describe('R.equals', () => {
  it('happy', () => {
    const result = equals(4, 1)
    result // $ExpectType boolean
  })
  it('with object', () => {
    const foo = {a: 1}
    const bar = {a: 2}
    const result = equals(foo, bar)
    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = equals(4)(1)

    result // $ExpectType boolean
  })
})

Lodash is fastest. Rambda is 58.37% slower and Ramda is 96.73% slower

const R = require('../../dist/rambda.js')

const limit = 10000

const strings = Array(limit)
  .fill(null)
  .map(() => Math.floor(Math.random() * 1000))

const equals = [
  {
    label: 'Rambda',
    fn: () => {
      strings.forEach(x => R.equals(x, 'ss'))
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      strings.forEach(x => Ramda.equals(x, 'ss'))
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      strings.forEach(x => _.isEqual(x, 'ss'))
    },
  },
]

evolve

evolve<T, U>(rules: ((x: T) => U)[], list: T[]): U[]

It takes object or array of functions as set of rules. These rules are applied to the iterable input to produce the result.

💥 Error handling of this method differs between Ramda and Rambda. Ramda for some wrong inputs returns result and for other - it returns one of the inputs. Rambda simply throws when inputs are not correct. Full details for this mismatch are listed in source/_snapshots/evolve.spec.js.snap file.

const rules = {
  foo : add(1),
  bar : add(-1),
}
const input = {
  a   : 1,
  foo : 2,
  bar : 3,
}
const result = evolve(rules, input)
const expected = {
  a   : 1,
  foo : 3,
  bar : 2,
})
// => `result` is equal to `expected`

Try this R.evolve example in Rambda REPL

All Typescript definitions

evolve<T, U>(rules: ((x: T) => U)[], list: T[]): U[];
evolve<T, U>(rules: ((x: T) => U)[]) : (list: T[]) => U[];
evolve<E extends Evolver, V extends Evolvable<E>>(rules: E, obj: V): Evolve<V, E>;
evolve<E extends Evolver>(rules: E): <V extends Evolvable<E>>(obj: V) => Evolve<V, E>;

R.evolve source

import {_isArray} from './_internals/_isArray'
import {mapArray, mapObject} from './map'
import {type} from './type'

export function evolveArray(rules, list) {
  return mapArray(
    (x, i) => {
      if (type(rules[i]) === 'Function') {
        return rules[i](x)
      }

      return x
    },
    list,
    true
  )
}

export function evolveObject(rules, iterable) {
  return mapObject((x, prop) => {
    if (type(x) === 'Object') {
      const typeRule = type(rules[prop])
      if (typeRule === 'Function') {
        return rules[prop](x)
      }
      if (typeRule === 'Object') {
        return evolve(rules[prop], x)
      }

      return x
    }
    if (type(rules[prop]) === 'Function') {
      return rules[prop](x)
    }

    return x
  }, iterable)
}

export function evolve(rules, iterable) {
  if (arguments.length === 1) {
    return _iterable => evolve(rules, _iterable)
  }
  const rulesType = type(rules)
  const iterableType = type(iterable)

  if (iterableType !== rulesType) {
    throw new Error('iterableType !== rulesType')
  }

  if (!['Object', 'Array'].includes(rulesType)) {
    throw new Error(
      `'iterable' and 'rules' are from wrong type ${rulesType}`
    )
  }

  if (iterableType === 'Object') {
    return evolveObject(rules, iterable)
  }

  return evolveArray(rules, iterable)
}

Tests

import {evolve as evolveRamda} from 'ramda'

import {add} from '../rambda'
import {compareCombinations, compareToRamda} from './_internals/testUtils'
import {evolve} from './evolve'

test('happy', () => {
  const rules = {
    foo: add(1),
    nested: {bar: x => Object.keys(x).length},
  }
  const input = {
    a: 1,
    foo: 2,
    nested: {bar: {z: 3}},
  }
  const result = evolve(rules, input)
  expect(result).toEqual({
    a: 1,
    foo: 3,
    nested: {bar: 1},
  })
})

test('nested rule is wrong', () => {
  const rules = {
    foo: add(1),
    nested: {bar: 10},
  }
  const input = {
    a: 1,
    foo: 2,
    nested: {bar: {z: 3}},
  }
  const result = evolve(rules)(input)
  expect(result).toEqual({
    a: 1,
    foo: 3,
    nested: {bar: {z: 3}},
  })
})

test('is recursive', () => {
  const rules = {
    nested: {
      second: add(-1),
      third: add(1),
    },
  }
  const object = {
    first: 1,
    nested: {
      second: 2,
      third: 3,
    },
  }
  const expected = {
    first: 1,
    nested: {
      second: 1,
      third: 4,
    },
  }
  const result = evolve(rules, object)
  expect(result).toEqual(expected)
})

test('ignores primitive values', () => {
  const rules = {
    n: 2,
    m: 'foo',
  }
  const object = {
    n: 0,
    m: 1,
  }
  const expected = {
    n: 0,
    m: 1,
  }
  const result = evolve(rules, object)
  expect(result).toEqual(expected)
})

test('with array', () => {
  const rules = [add(1), add(-1)]
  const list = [100, 1400]
  const expected = [101, 1399]
  const result = evolve(rules, list)
  expect(result).toEqual(expected)
})

const rulesObject = {a: add(1)}
const rulesList = [add(1)]
const possibleIterables = [null, undefined, '', 42, [], [1], {a: 1}]
const possibleRules = [...possibleIterables, rulesList, rulesObject]

describe('brute force', () => {
  compareCombinations({
    firstInput: possibleRules,
    callback: errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        Object {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 4,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 51,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 63,
        }
      `)
    },
    secondInput: possibleIterables,
    fn: evolve,
    fnRamda: evolveRamda,
  })
})

Typescript test

import {evolve, add} from 'rambda'

describe('R.evolve', () => {
  it('happy', () => {
    const input = {
      foo: 2,
      nested: {
        a: 1,
        bar: 3,
      },
    }
    const rules = {
      foo: add(1),
      nested: {
        a: add(-1),
        bar: add(1),
      },
    }
    const result = evolve(rules, input)
    const curriedResult = evolve(rules)(input)

    result.nested.a // $ExpectType number
    curriedResult.nested.a // $ExpectType number
    result.nested.bar // $ExpectType number
    result.foo // $ExpectType number
  })
  it('with array', () => {
    const rules = [String, String]
    const input = [100, 1400]
    const result = evolve(rules, input)
    const curriedResult = evolve(rules)(input)
    result // $ExpectType string[]
    curriedResult // $ExpectType string[]
  })
})

F

F(): boolean

F() // => false

Try this R.F example in Rambda REPL

All Typescript definitions

F(): boolean;

R.F source

export function F() {
  return false
}

filter

filter<T>(predicate: Predicate<T>): (input: T[]) => T[]

It filters list or object input using a predicate function.

const list = [3, 4, 3, 2]
const listPredicate = x => x > 2

const object = {abc: 'fo', xyz: 'bar', baz: 'foo'}
const objectPredicate = (x, prop) => x.length + prop.length > 5

const result = [
  R.filter(listPredicate, list),
  R.filter(objectPredicate, object)
]
// => [ [3, 4], { xyz: 'bar', baz: 'foo'} ]

Try this R.filter example in Rambda REPL

All Typescript definitions

filter<T>(predicate: Predicate<T>): (input: T[]) => T[];
filter<T>(predicate: Predicate<T>, input: T[]): T[];
filter<T, U>(predicate: ObjectPredicate<T>): (x: Dictionary<T>) => Dictionary<T>;
filter<T>(predicate: ObjectPredicate<T>, x: Dictionary<T>): Dictionary<T>;

R.filter source

import {_isArray} from './_internals/_isArray'

export function filterObject(predicate, obj) {
  const willReturn = {}

  for (const prop in obj) {
    if (predicate(obj[prop], prop, obj)) {
      willReturn[prop] = obj[prop]
    }
  }

  return willReturn
}

export function filterArray(predicate, list, indexed = false) {
  let index = 0
  const len = list.length
  const willReturn = []

  while (index < len) {
    const predicateResult = indexed
      ? predicate(list[index], index)
      : predicate(list[index])
    if (predicateResult) {
      willReturn.push(list[index])
    }

    index++
  }

  return willReturn
}

export function filter(predicate, iterable) {
  if (arguments.length === 1)
    return _iterable => filter(predicate, _iterable)
  if (!iterable) {
    throw new Error('Incorrect iterable input')
  }

  if (_isArray(iterable)) return filterArray(predicate, iterable, false)

  return filterObject(predicate, iterable)
}

Tests

import {T} from './T'
import {filter} from './filter'
import {filter as filterRamda} from 'ramda'

const sampleObject = {
  a: 1,
  b: 2,
  c: 3,
  d: 4,
}

test('happy', () => {
  const isEven = n => n % 2 === 0

  expect(filter(isEven, [1, 2, 3, 4])).toEqual([2, 4])
  expect(
    filter(isEven, {
      a: 1,
      b: 2,
      d: 3,
    })
  ).toEqual({b: 2})
})

test('predicate when input is object', () => {
  const obj = {
    a: 1,
    b: 2,
  }
  const predicate = (val, prop, inputObject) => {
    expect(inputObject).toEqual(obj)
    expect(typeof prop).toEqual('string')

    return val < 2
  }
  expect(filter(predicate, obj)).toEqual({a: 1})
})

test('with object', () => {
  const isEven = n => n % 2 === 0
  const result = filter(isEven, sampleObject)
  const expectedResult = {
    b: 2,
    d: 4,
  }

  expect(result).toEqual(expectedResult)
})

test('bad inputs difference between Ramda and Rambda', () => {
  expect(() => filter(T, null)).toThrowWithMessage(
    Error,
    `Incorrect iterable input`
  )
  expect(() => filter(T)(undefined)).toThrowWithMessage(
    Error,
    `Incorrect iterable input`
  )
  expect(() => filterRamda(T, null)).toThrowWithMessage(
    TypeError,
    `Cannot read properties of null (reading 'filter')`
  )
  expect(() => filterRamda(T, undefined)).toThrowWithMessage(
    TypeError,
    `Cannot read properties of undefined (reading 'filter')`
  )
})

Typescript test

import {filter} from 'rambda'

const list = [1, 2, 3]
const obj = {a: 1, b: 2}

describe('R.filter with array', () => {
  it('happy', () => {
    const result = filter<number>(x => {
      x // $ExpectType number
      return x > 1
    }, list)
    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = filter<number>(x => {
      x // $ExpectType number
      return x > 1
    })(list)
    result // $ExpectType number[]
  })
})

describe('R.filter with objects', () => {
  it('happy', () => {
    const result = filter<number>((val, prop, origin) => {
      val // $ExpectType number
      prop // $ExpectType string
      origin // $ExpectType Dictionary<number>

      return val > 1
    }, obj)
    result // $ExpectType Dictionary<number>
  })
  it('curried version requires second dummy type', () => {
    const result = filter<number, any>((val, prop, origin) => {
      val // $ExpectType number
      prop // $ExpectType string
      origin // $ExpectType Dictionary<number>

      return val > 1
    })(obj)
    result // $ExpectType Dictionary<number>
  })
})

Lodash is fastest. Rambda is 6.7% slower and Ramda is 72.03% slower

const R = require('../../dist/rambda.js')

const arr = [1, 2, 3, 4]
const fn = x => x > 2
const filter = [
  {
    label: 'Rambda',
    fn: () => {
      R.filter(fn, arr)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.filter(fn, arr)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.filter(arr, fn)
    },
  },
]

find

find<T>(predicate: (x: T) => boolean, list: T[]): T | undefined

It returns the first element of list that satisfy the predicate.

If there is no such element, it returns undefined.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.find(predicate, list)
// => {foo: 1}

Try this R.find example in Rambda REPL

All Typescript definitions

find<T>(predicate: (x: T) => boolean, list: T[]): T | undefined;
find<T>(predicate: (x: T) => boolean): (list: T[]) => T | undefined;

R.find source

export function find(predicate, list) {
  if (arguments.length === 1) return _list => find(predicate, _list)

  let index = 0
  const len = list.length

  while (index < len) {
    const x = list[index]
    if (predicate(x)) {
      return x
    }

    index++
  }
}

Tests

import {find} from './find'
import {propEq} from './propEq'

const list = [{a: 1}, {a: 2}, {a: 3}]

test('happy', () => {
  const fn = propEq('a', 2)
  expect(find(fn, list)).toEqual({a: 2})
})

test('with curry', () => {
  const fn = propEq('a', 4)
  expect(find(fn)(list)).toBeUndefined()
})

test('with empty list', () => {
  expect(find(() => true, [])).toBeUndefined()
})

Typescript test

import {find} from 'rambda'

const list = [1, 2, 3]

describe('R.find', () => {
  it('happy', () => {
    const predicate = (x: number) => x > 2
    const result = find(predicate, list)
    result // $ExpectType number | undefined
  })
  it('curried', () => {
    const predicate = (x: number) => x > 2
    const result = find(predicate)(list)
    result // $ExpectType number | undefined
  })
})

Rambda is fastest. Ramda is 85.14% slower and Lodash is 42.65% slower

const R = require('../../dist/rambda.js')

const fn = x => x > 2
const list = [1, 2, 3, 4]

const find = [
  {
    label: 'Rambda',
    fn: () => {
      R.find(fn, list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.find(fn, list)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.find(list, fn)
    },
  },
]

findIndex

findIndex<T>(predicate: (x: T) => boolean, list: T[]): number

It returns the index of the first element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 'bar'}, {foo: 1}]

const result = R.findIndex(predicate, list)
// => 1

Try this R.findIndex example in Rambda REPL

All Typescript definitions

findIndex<T>(predicate: (x: T) => boolean, list: T[]): number;
findIndex<T>(predicate: (x: T) => boolean): (list: T[]) => number;

R.findIndex source

export function findIndex(predicate, list) {
  if (arguments.length === 1) return _list => findIndex(predicate, _list)

  const len = list.length
  let index = -1

  while (++index < len) {
    if (predicate(list[index])) {
      return index
    }
  }

  return -1
}

Tests

import {findIndex} from './findIndex'
import {propEq} from './propEq'

const list = [{a: 1}, {a: 2}, {a: 3}]

test('happy', () => {
  expect(findIndex(propEq('a', 2), list)).toEqual(1)

  expect(findIndex(propEq('a', 1))(list)).toEqual(0)

  expect(findIndex(propEq('a', 4))(list)).toEqual(-1)
})

Typescript test

import {findIndex} from 'rambda'

const list = [1, 2, 3]

describe('R.findIndex', () => {
  it('happy', () => {
    const predicate = (x: number) => x > 2
    const result = findIndex(predicate, list)
    result // $ExpectType number
  })
  it('curried', () => {
    const predicate = (x: number) => x > 2
    const result = findIndex(predicate)(list)
    result // $ExpectType number
  })
})

Rambda is fastest. Ramda is 86.48% slower and Lodash is 72.27% slower

const R = require('../../dist/rambda.js')

const fn = x => x > 2
const list = [1, 2, 3, 4]

const findIndex = [
  {
    label: 'Rambda',
    fn: () => {
      R.findIndex(fn, list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.findIndex(fn, list)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.findIndex(list, fn)
    },
  },
]

findLast

findLast<T>(fn: (x: T) => boolean, list: T[]): T | undefined

It returns the last element of list satisfying the predicate function.

If there is no such element, then undefined is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLast(predicate, list)
// => {foo: 1}

Try this R.findLast example in Rambda REPL

All Typescript definitions

findLast<T>(fn: (x: T) => boolean, list: T[]): T | undefined;
findLast<T>(fn: (x: T) => boolean): (list: T[]) => T | undefined;

R.findLast source

export function findLast(predicate, list) {
  if (arguments.length === 1) return _list => findLast(predicate, _list)

  let index = list.length

  while (--index >= 0) {
    if (predicate(list[index])) {
      return list[index]
    }
  }

  return undefined
}

Tests

import {findLast} from './findLast'

test('happy', () => {
  const result = findLast(x => x > 1, [1, 1, 1, 2, 3, 4, 1])
  expect(result).toEqual(4)

  expect(findLast(x => x === 0, [0, 1, 1, 2, 3, 4, 1])).toEqual(0)
})

test('with curry', () => {
  expect(findLast(x => x > 1)([1, 1, 1, 2, 3, 4, 1])).toEqual(4)
})

const obj1 = {x: 100}
const obj2 = {x: 200}
const a = [11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0]
const even = function (x) {
  return x % 2 === 0
}
const gt100 = function (x) {
  return x > 100
}
const isStr = function (x) {
  return typeof x === 'string'
}
const xGt100 = function (o) {
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLast(even, a)).toEqual(0)
  expect(findLast(gt100, a)).toEqual(300)
  expect(findLast(isStr, a)).toEqual('cow')
  expect(findLast(xGt100, a)).toEqual(obj2)
})

test('ramda 2', () => {
  expect(findLast(even, ['zing'])).toEqual(undefined)
})

test('ramda 3', () => {
  expect(findLast(even, [2, 3, 5])).toEqual(2)
})

test('ramda 4', () => {
  expect(findLast(even, [])).toEqual(undefined)
})

Typescript test

import {findLast} from 'rambda'

const list = [1, 2, 3]

describe('R.findLast', () => {
  it('happy', () => {
    const predicate = (x: number) => x > 2
    const result = findLast(predicate, list)
    result // $ExpectType number | undefined
  })
  it('curried', () => {
    const predicate = (x: number) => x > 2
    const result = findLast(predicate)(list)
    result // $ExpectType number | undefined
  })
})

findLastIndex

findLastIndex<T>(predicate: (x: T) => boolean, list: T[]): number

It returns the index of the last element of list satisfying the predicate function.

If there is no such element, then -1 is returned.

const predicate = x => R.type(x.foo) === 'Number'
const list = [{foo: 0}, {foo: 1}]

const result = R.findLastIndex(predicate, list)
// => 1

Try this R.findLastIndex example in Rambda REPL

All Typescript definitions

findLastIndex<T>(predicate: (x: T) => boolean, list: T[]): number;
findLastIndex<T>(predicate: (x: T) => boolean): (list: T[]) => number;

R.findLastIndex source

export function findLastIndex(fn, list) {
  if (arguments.length === 1) return _list => findLastIndex(fn, _list)

  let index = list.length

  while (--index >= 0) {
    if (fn(list[index])) {
      return index
    }
  }

  return -1
}

Tests

import {findLastIndex} from './findLastIndex'

test('happy', () => {
  const result = findLastIndex(x => x > 1, [1, 1, 1, 2, 3, 4, 1])

  expect(result).toEqual(5)

  expect(findLastIndex(x => x === 0, [0, 1, 1, 2, 3, 4, 1])).toEqual(0)
})

test('with curry', () => {
  expect(findLastIndex(x => x > 1)([1, 1, 1, 2, 3, 4, 1])).toEqual(5)
})

const obj1 = {x: 100}
const obj2 = {x: 200}
const a = [11, 10, 9, 'cow', obj1, 8, 7, 100, 200, 300, obj2, 4, 3, 2, 1, 0]
const even = function (x) {
  return x % 2 === 0
}
const gt100 = function (x) {
  return x > 100
}
const isStr = function (x) {
  return typeof x === 'string'
}
const xGt100 = function (o) {
  return o && o.x > 100
}

test('ramda 1', () => {
  expect(findLastIndex(even, a)).toEqual(15)
  expect(findLastIndex(gt100, a)).toEqual(9)
  expect(findLastIndex(isStr, a)).toEqual(3)
  expect(findLastIndex(xGt100, a)).toEqual(10)
})

test('ramda 2', () => {
  expect(findLastIndex(even, ['zing'])).toEqual(-1)
})

test('ramda 3', () => {
  expect(findLastIndex(even, [2, 3, 5])).toEqual(0)
})

test('ramda 4', () => {
  expect(findLastIndex(even, [])).toEqual(-1)
})

Typescript test

import {findLastIndex} from 'rambda'

const list = [1, 2, 3]

describe('R.findLastIndex', () => {
  it('happy', () => {
    const predicate = (x: number) => x > 2
    const result = findLastIndex(predicate, list)
    result // $ExpectType number
  })
  it('curried', () => {
    const predicate = (x: number) => x > 2
    const result = findLastIndex(predicate)(list)
    result // $ExpectType number
  })
})

flatten

flatten<T>(list: any[]): T[]

It deeply flattens an array.

const result = R.flatten([
  1, 
  2, 
  [3, 30, [300]], 
  [4]
])
// => [ 1, 2, 3, 30, 300, 4 ]

Try this R.flatten example in Rambda REPL

All Typescript definitions

flatten<T>(list: any[]): T[];

R.flatten source

import {_isArray} from './_internals/_isArray'

export function flatten(list, input) {
  const willReturn = input === undefined ? [] : input

  for (let i = 0; i < list.length; i++) {
    if (_isArray(list[i])) {
      flatten(list[i], willReturn)
    } else {
      willReturn.push(list[i])
    }
  }

  return willReturn
}

Tests

import {flatten} from './flatten'

test('happy', () => {
  expect(flatten([1, 2, 3, [[[[[4]]]]]])).toEqual([1, 2, 3, 4])

  expect(flatten([1, [2, [[3]]], [4]])).toEqual([1, 2, 3, 4])

  expect(flatten([1, [2, [[[3]]]], [4]])).toEqual([1, 2, 3, 4])

  expect(flatten([1, 2, [3, 4], 5, [6, [7, 8, [9, [10, 11], 12]]]])).toEqual(
    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
  )
})

test('readme example', () => {
  const result = flatten([1, 2, [3, 30, [300]], [4]])
  expect(result).toEqual([1, 2, 3, 30, 300, 4])
})

Typescript test

import {flatten} from 'rambda'

describe('flatten', () => {
  it('happy', () => {
    const result = flatten<number>([1, 2, [3, [4]]])
    result // $ExpectType number[]
  })
})

Rambda is fastest. Ramda is 95.26% slower and Lodash is 10.27% slower

const R = require('../../dist/rambda.js')

const list = [1, [2, [3, 4, 6]]]

const flatten = [
  {
    label: 'Rambda',
    fn: () => {
      R.flatten(list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.flatten(list)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.flatten(list)
    },
  },
]

flip

It returns function which calls fn with exchanged first and second argument.

💥 Rambda's flip will throw if the arity of the input function is greater or equal to 5.

const subtractFlip = R.flip(R.subtract)

const result = [
  subtractFlip(1,7),
  R.subtract(1, 6)
]  
// => [6, -6]

Try this R.flip example in Rambda REPL

forEach

forEach<T>(fn: Iterator<T, void>, list: T[]): T[]

It applies iterable function over all members of list and returns list.

💥 It works with objects, unlike Ramda.

const sideEffect = {}
const result = R.forEach(
  x => sideEffect[`foo${x}`] = x
)([1, 2])

sideEffect // => {foo1: 1, foo2: 2}
result // => [1, 2]

Try this R.forEach example in Rambda REPL

All Typescript definitions

forEach<T>(fn: Iterator<T, void>, list: T[]): T[];
forEach<T>(fn: Iterator<T, void>): (list: T[]) => T[];
forEach<T>(fn: ObjectIterator<T, void>, list: Dictionary<T>): Dictionary<T>;
forEach<T, U>(fn: ObjectIterator<T, void>): (list: Dictionary<T>) => Dictionary<T>;

R.forEach source

import {_isArray} from './_internals/_isArray'
import {_keys} from './_internals/_keys'

export function forEach(fn, list) {
  if (arguments.length === 1) return _list => forEach(fn, _list)

  if (list === undefined) {
    return
  }

  if (_isArray(list)) {
    let index = 0
    const len = list.length

    while (index < len) {
      fn(list[index])
      index++
    }
  } else {
    let index = 0
    const keys = _keys(list)
    const len = keys.length

    while (index < len) {
      const key = keys[index]
      fn(list[key], key, list)
      index++
    }
  }

  return list
}

Tests

import {forEach} from './forEach'
import {type} from './type'

test('happy', () => {
  const sideEffect = {}
  forEach(x => (sideEffect[`foo${x}`] = x + 10))([1, 2])

  expect(sideEffect).toEqual({
    foo1: 11,
    foo2: 12,
  })
})

test('iterate over object', () => {
  const obj = {
    a: 1,
    b: [1, 2],
    c: {d: 7},
    f: 'foo',
  }
  const result = {}
  const returned = forEach((val, prop, inputObj) => {
    expect(type(inputObj)).toBe('Object')
    result[prop] = `${prop}-${type(val)}`
  })(obj)

  const expected = {
    a: 'a-Number',
    b: 'b-Array',
    c: 'c-Object',
    f: 'f-String',
  }

  expect(result).toEqual(expected)
  expect(returned).toEqual(obj)
})

test('with empty list', () => {
  const list = []
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

test('with wrong input', () => {
  const list = undefined
  const result = forEach(x => x * x)(list)

  expect(result).toBeUndefined()
})

test('returns the input', () => {
  const list = [1, 2, 3]
  const result = forEach(x => x * x)(list)

  expect(result).toEqual(list)
})

Typescript test

import {forEach} from 'rambda'

const list = [1, 2, 3]
const obj = {a: 1, b: 2}

describe('R.forEach with arrays', () => {
  it('happy', () => {
    const result = forEach(a => {
      a // $ExpectType number
    }, list)
    result // $ExpectType number[]
  })
  it('curried require an explicit typing', () => {
    const result = forEach<number>(a => {
      a // $ExpectType number
    })(list)
    result // $ExpectType number[]
  })
})

describe('R.forEach with objects', () => {
  it('happy', () => {
    const result = forEach((a, b, c) => {
      a // $ExpectType number
      b // $ExpectType string
      c // $ExpectType Dictionary<number>
      return `${a}`
    }, obj)
    result // $ExpectType Dictionary<number>
  })
  it('curried require an input typing and a dummy third typing', () => {
    // Required in order all typings to work
    const result = forEach<number, any>((a, b, c) => {
      a // $ExpectType number
      b // $ExpectType string
      c // $ExpectType Dictionary<number>
    })(obj)
    result // $ExpectType Dictionary<number>
  })
  it('iterator without property', () => {
    const result = forEach(a => {
      a // $ExpectType number
    }, obj)
    result // $ExpectType Dictionary<number>
  })
})

fromPairs

It transforms a listOfPairs to an object.

const listOfPairs = [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', [ 3, 4 ] ] ]
const expected = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}

const result = R.fromPairs(listOfPairs)
// => `result` is equal to `expected`

Try this R.fromPairs example in Rambda REPL

groupBy

It splits list according to a provided groupFn function and returns an object.

const list = [ 'a', 'b', 'aa', 'bb' ]
const groupFn = x => x.length

const result = R.groupBy(groupFn, list)
// => { '1': ['a', 'b'], '2': ['aa', 'bb'] }

Try this R.groupBy example in Rambda REPL

groupWith

It returns separated version of list or string input, where separation is done with equality compareFn function.

const compareFn = (x, y) => x === y
const list = [1, 2, 2, 1, 1, 2]

const result = R.groupWith(isConsecutive, list)
// => [[1], [2,2], [1,1], [2]]

Try this R.groupWith example in Rambda REPL

has

has<T>(prop: string, obj: T): boolean

It returns true if obj has property prop.

const obj = {a: 1}

const result = [
  R.has('a', obj),
  R.has('b', obj)
]
// => [true, false]

Try this R.has example in Rambda REPL

All Typescript definitions

has<T>(prop: string, obj: T): boolean;
has(prop: string): <T>(obj: T) => boolean;

R.has source

export function has(prop, obj) {
  if (arguments.length === 1) return _obj => has(prop, _obj)

  if (!obj) return false

  return obj.hasOwnProperty(prop)
}

Tests

import {has} from './has'

test('happy', () => {
  expect(has('a')({a: 1})).toBeTrue()
  expect(has('b', {a: 1})).toBeFalse()
})

test('with non-object', () => {
  expect(has('a', undefined)).toEqual(false)
  expect(has('a', null)).toEqual(false)
  expect(has('a', true)).toEqual(false)
  expect(has('a', '')).toEqual(false)
  expect(has('a', /a/)).toEqual(false)
})

Typescript test

import {has} from 'rambda'

describe('R.has', () => {
  it('happy', () => {
    const result = has('foo', {a: 1})
    const curriedResult = has('bar')({a: 1})
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

hasPath

hasPath<T>(
  path: string | string[],
  input: object
): boolean

It will return true, if input object has truthy path(calculated with R.path).

const path = 'a.b'
const pathAsArray = ['a', 'b']
const obj = {a: {b: []}}

const result = [
  R.hasPath(path, obj),
  R.hasPath(pathAsArray, obj),
  R.hasPath('a.c', obj),
]
// => [true, true, false]

Try this R.hasPath example in Rambda REPL

All Typescript definitions

hasPath<T>(
  path: string | string[],
  input: object
): boolean;
hasPath<T>(
  path: string | string[]
): (input: object) => boolean;

R.hasPath source

import {path} from './path'

export function hasPath(pathInput, obj) {
  if (arguments.length === 1) {
    return objHolder => hasPath(pathInput, objHolder)
  }

  return path(pathInput, obj) !== undefined
}

Tests

import {hasPath} from './hasPath'

test('when true', () => {
  const path = 'a.b'
  const obj = {a: {b: []}}

  const result = hasPath(path)(obj)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('when false', () => {
  const path = 'a.b'
  const obj = {}

  const result = hasPath(path, obj)
  const expectedResult = false

  expect(result).toEqual(expectedResult)
})

Typescript test

import {hasPath} from 'rambda'

describe('R.hasPath', () => {
  it('string path', () => {
    const obj = {a: {b: 1}}
    const result = hasPath('a.b', obj)
    const curriedResult = hasPath('a.c')(obj)
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
  it('array path', () => {
    const obj = {a: {b: 1}}
    const result = hasPath(['a', 'b'], obj)
    const curriedResult = hasPath(['a', 'c'])(obj)
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

head

head(input: string): string

It returns the first element of list or string input.

const result = [
  R.head([1, 2, 3]),
  R.head('foo') 
]
// => [1, 'f']

Try this R.head example in Rambda REPL

All Typescript definitions

head(input: string): string;
head(emptyList: []): undefined;
head<T>(input: T[]): T | undefined;

R.head source

export function head(listOrString) {
  if (typeof listOrString === 'string') return listOrString[0] || ''

  return listOrString[0]
}

Tests

import {head} from './head'

test('head', () => {
  expect(head(['fi', 'fo', 'fum'])).toEqual('fi')
  expect(head([])).toEqual(undefined)
  expect(head('foo')).toEqual('f')
  expect(head('')).toEqual('')
})

Typescript test

import {head} from 'rambda'

describe('R.head', () => {
  it('string', () => {
    const result = head('foo')
    result // $ExpectType string
  })

  it('array', () => {
    const result = head([1, 2, 3])
    result // $ExpectType number | undefined
  })

  it('empty array - case 1', () => {
    const result = head([])
    result // $ExpectType undefined
  })
  it('empty array - case 2', () => {
    const list = ['foo', 'bar'].filter(x => x.startsWith('a'))
    const result = head(list)
    result // $ExpectType string | undefined
  })
})

identical

It returns true if its arguments a and b are identical.

Otherwise, it returns false.

💥 Values are identical if they reference the same memory. NaN is identical to NaN; 0 and -0 are not identical.

const objA = {a: 1};
const objB = {a: 1};
R.identical(objA, objA); // => true
R.identical(objA, objB); // => false
R.identical(1, 1); // => true
R.identical(1, '1'); // => false
R.identical([], []); // => false
R.identical(0, -0); // => false
R.identical(NaN, NaN); // => true

Try this R.identical example in Rambda REPL

identity

identity<T>(input: T): T

It just passes back the supplied input argument.

💥 Logic

R.identity(7) // => 7

Try this R.identity example in Rambda REPL

All Typescript definitions

identity<T>(input: T): T;

R.identity source

export function identity(x) {
  return x
}

Tests

import {identity} from './identity'

test('happy', () => {
  expect(identity(7)).toEqual(7)
  expect(identity(true)).toEqual(true)
  expect(identity({a: 1})).toEqual({a: 1})
})

Typescript test

import {identity} from 'rambda'

describe('R.identity', () => {
  it('happy', () => {
    const result = identity(4)
    result // $ExpectType 4
  })
})

ifElse

ifElse<TArgs extends any[], TOnTrueResult, TOnFalseResult>(fn: (...args: TArgs) => boolean, onTrue: (...args: TArgs) => TOnTrueResult, onFalse: (...args: TArgs) => TOnFalseResult): (...args: TArgs) => TOnTrueResult | TOnFalseResult

It expects condition, onTrue and onFalse functions as inputs and it returns a new function with example name of fn.

When fn`` is called with inputargument, it will return eitheronTrue(input)oronFalse(input)depending oncondition(input)` evaluation.

const fn = R.ifElse(
 x => x>10,
 x => x*2,
 x => x*10
)

const result = [ fn(8), fn(18) ]
// => [80, 36]

Try this R.ifElse example in Rambda REPL

All Typescript definitions

ifElse<TArgs extends any[], TOnTrueResult, TOnFalseResult>(fn: (...args: TArgs) => boolean, onTrue: (...args: TArgs) => TOnTrueResult, onFalse: (...args: TArgs) => TOnFalseResult): (...args: TArgs) => TOnTrueResult | TOnFalseResult;

R.ifElse source

import {curry} from './curry'

function ifElseFn(condition, onTrue, onFalse) {
  return (...input) => {
    const conditionResult =
      typeof condition === 'boolean' ? condition : condition(...input)

    if (conditionResult === true) {
      return onTrue(...input)
    }

    return onFalse(...input)
  }
}

export const ifElse = curry(ifElseFn)

Tests

import {always} from './always'
import {has} from './has'
import {identity} from './identity'
import {ifElse} from './ifElse'
import {prop} from './prop'

const condition = has('foo')
const v = function (a) {
  return typeof a === 'number'
}
const t = function (a) {
  return a + 1
}
const ifFn = x => prop('foo', x).length
const elseFn = () => false

test('happy', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({foo: 'bar'})).toEqual(3)
  expect(fn({fo: 'bar'})).toEqual(false)
})

test('ramda spec', () => {
  const ifIsNumber = ifElse(v)
  expect(ifIsNumber(t, identity)(15)).toEqual(16)
  expect(ifIsNumber(t, identity)('hello')).toEqual('hello')
})

test('pass all arguments', () => {
  const identity = function (a) {
    return a
  }
  const v = function () {
    return true
  }
  const onTrue = function (a, b) {
    expect(a).toEqual(123)
    expect(b).toEqual('abc')
  }
  ifElse(v, onTrue, identity)(123, 'abc')
})

test('accept constant as condition', () => {
  const fn = ifElse(true)(always(true))(always(false))

  expect(fn()).toEqual(true)
})

test('accept constant as condition - case 2', () => {
  const fn = ifElse(false, always(true), always(false))

  expect(fn()).toEqual(false)
})

test('curry 1', () => {
  const fn = ifElse(condition, ifFn)(elseFn)

  expect(fn({foo: 'bar'})).toEqual(3)
  expect(fn({fo: 'bar'})).toEqual(false)
})

test('curry 2', () => {
  const fn = ifElse(condition)(ifFn)(elseFn)

  expect(fn({foo: 'bar'})).toEqual(3)
  expect(fn({fo: 'bar'})).toEqual(false)
})

test('simple arity of 1', () => {
  const condition = x => x > 5
  const onTrue = x => x + 1
  const onFalse = x => x + 10
  const result = ifElse(condition, onTrue, onFalse)(1)
  expect(result).toBe(11)
})

test('simple arity of 2', () => {
  const condition = (x, y) => x + y > 5
  const onTrue = (x, y) => x + y + 1
  const onFalse = (x, y) => x + y + 10
  const result = ifElse(condition, onTrue, onFalse)(1, 10)
  expect(result).toBe(12)
})

Typescript test

import {ifElse} from 'rambda'

describe('R.ifElse', () => {
  it('happy', () => {
    const condition = (x: number) => x > 5
    const onTrue = (x: number) => `foo${x}`
    const onFalse = (x: number) => `bar${x}`
    const fn = ifElse(condition, onTrue, onFalse)
    fn // $ExpectType (x: number) => string
    const result = fn(3)
    result // $ExpectType string
  })
  it('arity of 2', () => {
    const condition = (x: number, y: string) => x + y.length > 5
    const onTrue = (x: number, y: string) => `foo${x}-${y}`
    const onFalse = (x: number, y: string) => `bar${x}-${y}`
    const fn = ifElse(condition, onTrue, onFalse)
    fn // $ExpectType (x: number, y: string) => string
    const result = fn(3, 'hello')
    result // $ExpectType string
  })
})

Rambda is faster than Ramda with 58.56%

const R = require('../../dist/rambda.js')

const condition = R.has('foo')
const v = function (a) {
  return typeof a === 'number'
}
const t = function (a) {
  return a + 1
}
const ifFn = x => R.prop('foo', x).length
const elseFn = () => false

const ifElse = [
  {
    label: 'Rambda',
    fn: () => {
      const fn = R.ifElse(condition, ifFn)(elseFn)

      fn({foo: 'bar'})
      fn({fo: 'bar'})

      const ifIsNumber = R.ifElse(v)
      ifIsNumber(t, R.identity)(15)
      ifIsNumber(t, R.identity)('hello')
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      const fn = Ramda.ifElse(condition, ifFn)(elseFn)

      fn({foo: 'bar'})
      fn({fo: 'bar'})

      const ifIsNumber = Ramda.ifElse(v)
      ifIsNumber(t, R.identity)(15)
      ifIsNumber(t, R.identity)('hello')
    },
  },
]

inc

It increments a number.

R.inc(1) // => 2

Try this R.inc example in Rambda REPL

includes

includes(valueToFind: string, input: string[] | string): boolean

If input is string, then this method work as native String.includes.

If input is array, then R.equals is used to define if valueToFind belongs to the list.

const result = [
  R.includes('oo', 'foo'),
  R.includes({a: 1}, [{a: 1}])
]
// => [true, true ]

Try this R.includes example in Rambda REPL

All Typescript definitions

includes(valueToFind: string, input: string[] | string): boolean;
includes(valueToFind: string): (input: string[] | string) => boolean;
includes<T>(valueToFind: T, input: T[]): boolean;
includes<T>(valueToFind: T): (input: T[]) => boolean;

R.includes source

import {_isArray} from './_internals/_isArray'
import {_indexOf} from './equals'

export function includes(valueToFind, iterable) {
  if (arguments.length === 1)
    return _iterable => includes(valueToFind, _iterable)
  if (typeof iterable === 'string') {
    return iterable.includes(valueToFind)
  }
  if (!iterable) {
    throw new TypeError(`Cannot read property \'indexOf\' of ${iterable}`)
  }
  if (!_isArray(iterable)) return false

  return _indexOf(valueToFind, iterable) > -1
}

Tests

import {includes} from './includes'
import {includes as includesRamda} from 'ramda'

test('with string as iterable', () => {
  const str = 'foo bar'

  expect(includes('bar')(str)).toBeTrue()
  expect(includesRamda('bar')(str)).toBeTrue()
  expect(includes('never', str)).toBeFalse()
  expect(includesRamda('never', str)).toBeFalse()
})

test('with array as iterable', () => {
  const arr = [1, 2, 3]

  expect(includes(2)(arr)).toBeTrue()
  expect(includesRamda(2)(arr)).toBeTrue()

  expect(includes(4, arr)).toBeFalse()
  expect(includesRamda(4, arr)).toBeFalse()
})

test('with list of objects as iterable', () => {
  const arr = [{a: 1}, {b: 2}, {c: 3}]

  expect(includes({c: 3}, arr)).toBeTrue()
  expect(includesRamda({c: 3}, arr)).toBeTrue()
})

test('with NaN', () => {
  const result = includes(NaN, [NaN])
  const ramdaResult = includesRamda(NaN, [NaN])
  expect(result).toBeTrue()
  expect(ramdaResult).toBeTrue()
})

test('with wrong input that does not throw', () => {
  const result = includes(1, /foo/g)
  const ramdaResult = includesRamda(1, /foo/g)
  expect(result).toBeFalse()
  expect(ramdaResult).toBeFalse()
})

test('throws on wrong input - match ramda behaviour', () => {
  expect(() => includes(2, null)).toThrowWithMessage(
    TypeError,
    "Cannot read property 'indexOf' of null"
  )
  expect(() => includesRamda(2, null)).toThrowWithMessage(
    TypeError,
    `Cannot read properties of null (reading 'indexOf')`
  )
  expect(() => includes(2, undefined)).toThrowWithMessage(
    TypeError,
    "Cannot read property 'indexOf' of undefined"
  )
  expect(() => includesRamda(2, undefined)).toThrowWithMessage(
    TypeError,
    `Cannot read properties of undefined (reading 'indexOf')`
  )
})

Typescript test

import {includes} from 'rambda'

const list = [{a: {b: '1'}}, {a: {c: '2'}}, {a: {b: '3'}}]

describe('R.includes', () => {
  it('happy', () => {
    const result = includes({a: {b: '1'}}, list)
    result // $ExpectType boolean
  })
  it('with string', () => {
    const result = includes('oo', 'foo')
    const curriedResult = includes('oo')('foo')

    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

Rambda is faster than Ramda with 84.63%

const R = require('../../dist/rambda.js')

const {
  uniqListOfStrings,
  uniqListOfBooleans,
  uniqListOfObjects,
  uniqListOfLists,
  listOfVariousTypes,
  rangeOfNumbers,
} = require('./_utils.js')

const limit = 100
const additionalModes = listOfVariousTypes.map(unknownType => [
  unknownType,
  uniqListOfLists(limit),
])

const modes = [
  [99, rangeOfNumbers(limit)],
  [200, rangeOfNumbers(limit)],
  ...additionalModes,
  ['zeppelin', uniqListOfStrings(limit)],
  [null, uniqListOfBooleans(limit)],
  [{foo: true, bar: true}, uniqListOfObjects(limit)],
  [1, uniqListOfLists(limit)],
  [[1], uniqListOfLists(limit)],
]

function applyBenchmark(fn, input) {
  return fn(input[0], input[1])
}

const tests = [
  {
    label: 'Rambda',
    fn: R.includes,
  },
  {
    label: 'Ramda',
    fn: Ramda.includes,
  },
]

indexBy

It generates object with properties provided by condition and values provided by list array.

If condition is a function, then all list members are passed through it.

If condition is a string, then all list members are passed through R.path(condition).

const list = [ {id: 10}, {id: 20} ]

const withFunction = R.indexBy(
  x => x.id,
  list
)
const withString = R.indexBy(
  'id',
  list
)
const result = [
  withFunction, 
  R.equals(withFunction, withString)
]
// => [ { 10: {id: 10}, 20: {id: 20} }, true ]

Try this R.indexBy example in Rambda REPL

indexOf

It returns the index of the first element of list equals to valueToFind.

If there is no such element, it returns -1.

💥 It uses R.equals for list of objects/arrays or native indexOf for any other case.

const list = [0, 1, 2, 3]

const result = [
  R.indexOf(2, list),
  R.indexOf(0, list)
]
// => [2, -1]

Try this R.indexOf example in Rambda REPL

init

init<T>(input: T[]): T[]

It returns all but the last element of list or string input.

const result = [
  R.init([1, 2, 3]) , 
  R.init('foo')  // => 'fo'
]
// => [[1, 2], 'fo']

Try this R.init example in Rambda REPL

All Typescript definitions

init<T>(input: T[]): T[];
init(input: string): string;

R.init source

import baseSlice from './_internals/baseSlice'

export function init(listOrString) {
  if (typeof listOrString === 'string') return listOrString.slice(0, -1)

  return listOrString.length ? baseSlice(listOrString, 0, -1) : []
}

Tests

import {init} from './init'

test('with array', () => {
  expect(init([1, 2, 3])).toEqual([1, 2])
  expect(init([1, 2])).toEqual([1])
  expect(init([1])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([])).toEqual([])
  expect(init([1])).toEqual([])
})

test('with string', () => {
  expect(init('foo')).toEqual('fo')
  expect(init('f')).toEqual('')
  expect(init('')).toEqual('')
})

Typescript test

import {init} from 'rambda'

describe('R.init', () => {
  it('with string', () => {
    const result = init('foo')

    result // $ExpectType string
  })
  it('with list', () => {
    const result = init([1, 2, 3])

    result // $ExpectType number[]
  })
})

Rambda is fastest. Ramda is 92.24% slower and Lodash is 13.3% slower

const R = require('../../dist/rambda.js')

const list = [1, 2, 3, 4]

const init = [
  {
    label: 'Rambda',
    fn: () => {
      R.init(list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.init(list)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.initial(list)
    },
  },
]

intersection

It loops throw listA and listB and returns the intersection of the two according to R.equals.

const listA = [ { id : 1 }, { id : 2 }, { id : 3 }, { id : 4 } ]
const listB = [ { id : 3 }, { id : 4 }, { id : 5 }, { id : 6 } ]

const result = intersection(listA, listB)
// => [{ id : 3 }, { id : 4 }]

Try this R.intersection example in Rambda REPL

intersperse

It adds a separator between members of list.

const list = [ 0, 1, 2, 3 ]
const separator = '|'
const result = intersperse(separator, list)
// => [0, '|', 1, '|', 2, '|', 3]

Try this R.intersperse example in Rambda REPL

is

It returns true if x is instance of targetPrototype.

const result = [
  R.is(String, 'foo'),  
  R.is(Array, 1)
]
// => [true, false]

Try this R.is example in Rambda REPL

isEmpty

isEmpty<T>(x: T): boolean

It returns true if x is empty.

const result = [
  R.isEmpty(''),
  R.isEmpty({ x : 0 })
]
// => [true, false]

Try this R.isEmpty example in Rambda REPL

All Typescript definitions

isEmpty<T>(x: T): boolean;

R.isEmpty source

import {type} from './type'

export function isEmpty(input) {
  const inputType = type(input)
  if (['Undefined', 'NaN', 'Number', 'Null'].includes(inputType))
    return false
  if (!input) return true

  if (inputType === 'Object') {
    return Object.keys(input).length === 0
  }

  if (inputType === 'Array') {
    return input.length === 0
  }

  return false
}

Tests

import {isEmpty} from './isEmpty'

test('happy', () => {
  expect(isEmpty(undefined)).toEqual(false)
  expect(isEmpty('')).toEqual(true)
  expect(isEmpty(null)).toEqual(false)
  expect(isEmpty(' ')).toEqual(false)
  expect(isEmpty(new RegExp(''))).toEqual(false)
  expect(isEmpty([])).toEqual(true)
  expect(isEmpty([[]])).toEqual(false)
  expect(isEmpty({})).toEqual(true)
  expect(isEmpty({x: 0})).toEqual(false)
  expect(isEmpty(0)).toEqual(false)
  expect(isEmpty(NaN)).toEqual(false)
  expect(isEmpty([''])).toEqual(false)
})

Typescript test

import {isEmpty} from 'rambda'

describe('R.isEmpty', () => {
  it('happy', () => {
    const result = isEmpty('foo')
    result // $ExpectType boolean
  })
})

Rambda is fastest. Ramda is 97.14% slower and Lodash is 54.99% slower

const R = require('../../dist/rambda.js')

const isEmpty = [
  {
    label: 'Rambda',
    fn: () => {
      R.isEmpty(undefined)
      R.isEmpty('')
      R.isEmpty(null)
      R.isEmpty(' ')
      R.isEmpty(new RegExp(''))
      R.isEmpty([])
      R.isEmpty([[]])
      R.isEmpty({})
      R.isEmpty({x: 0})
      R.isEmpty(0)
      R.isEmpty(NaN)
      R.isEmpty([''])
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.isEmpty(undefined)
      Ramda.isEmpty('')
      Ramda.isEmpty(null)
      Ramda.isEmpty(' ')
      Ramda.isEmpty(new RegExp(''))
      Ramda.isEmpty([])
      Ramda.isEmpty([[]])
      Ramda.isEmpty({})
      Ramda.isEmpty({x: 0})
      Ramda.isEmpty(0)
      Ramda.isEmpty(NaN)
      Ramda.isEmpty([''])
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.isEmpty(undefined)
      _.isEmpty('')
      _.isEmpty(null)
      _.isEmpty(' ')
      _.isEmpty(new RegExp(''))
      _.isEmpty([])
      _.isEmpty([[]])
      _.isEmpty({})
      _.isEmpty({x: 0})
      _.isEmpty(0)
      _.isEmpty(NaN)
      _.isEmpty([''])
    },
  },
]

isNil

isNil(x: any): x is null | undefined

It returns true if x is either null or undefined.

const result = [
  R.isNil(null),
  R.isNil(1),
]
// => [true, false]

Try this R.isNil example in Rambda REPL

All Typescript definitions

isNil(x: any): x is null | undefined;

R.isNil source

export function isNil(x) {
  return x === undefined || x === null
}

Tests

import {isNil} from './isNil'

test('happy', () => {
  expect(isNil(null)).toBeTrue()

  expect(isNil(undefined)).toBeTrue()

  expect(isNil([])).toBeFalse()
})

join

join<T>(glue: string, list: T[]): string

It returns a string of all list instances joined with a glue.

R.join('-', [1, 2, 3])  // => '1-2-3'

Try this R.join example in Rambda REPL

All Typescript definitions

join<T>(glue: string, list: T[]): string;
join<T>(glue: string): (list: T[]) => string;

R.join source

export function join(glue, list) {
  if (arguments.length === 1) return _list => join(glue, _list)

  return list.join(glue)
}

Tests

import {join} from './join'

test('curry', () => {
  expect(join('|')(['foo', 'bar', 'baz'])).toEqual('foo|bar|baz')

  expect(join('|', [1, 2, 3])).toEqual('1|2|3')

  const spacer = join(' ')

  expect(spacer(['a', 2, 3.4])).toEqual('a 2 3.4')
})

Typescript test

import {join} from 'rambda'

describe('R.join', () => {
  it('happy', () => {
    const result = join('|', [1, 2, 3])
    result // $ExpectType string
  })
})

keys

keys<T extends object>(x: T): (keyof T)[]

It applies Object.keys over x and returns its keys.

R.keys({a:1, b:2})  // => ['a', 'b']

Try this R.keys example in Rambda REPL

All Typescript definitions

keys<T extends object>(x: T): (keyof T)[];
keys<T>(x: T): string[];

R.keys source

export function keys(x) {
  return Object.keys(x)
}

Tests

import {keys} from './keys'

test('happy', () => {
  expect(keys({a: 1})).toEqual(['a'])
})

Typescript test

import {keys} from 'rambda'

const obj = {a: 1, b: 2}

describe('R.keys', () => {
  it('happy', () => {
    const result = keys(obj)
    result // $ExpectType ("b" | "a")[]
  })
})

last

last(str: string): string

It returns the last element of input, as the input can be either a string or an array.

const result = [
  R.last([1, 2, 3]),
  R.last('foo'),
]
// => [3, 'o']

Try this R.last example in Rambda REPL

All Typescript definitions

last(str: string): string;
last(emptyList: []): undefined;
last<T extends any>(list: T[]): T | undefined;

R.last source

export function last(listOrString) {
  if (typeof listOrString === 'string') {
    return listOrString[listOrString.length - 1] || ''
  }

  return listOrString[listOrString.length - 1]
}

Tests

import {last} from './last'

test('with list', () => {
  expect(last([1, 2, 3])).toBe(3)
  expect(last([])).toBeUndefined()
})

test('with string', () => {
  expect(last('abc')).toEqual('c')
  expect(last('')).toEqual('')
})

Typescript test

import {last} from 'rambda'

describe('R.last', () => {
  it('string', () => {
    const result = last('foo')
    result // $ExpectType string
  })

  it('array', () => {
    const result = last([1, 2, 3])
    result // $ExpectType number | undefined
  })

  it('empty array - case 1', () => {
    const result = last([])
    result // $ExpectType undefined
  })
  it('empty array - case 2', () => {
    const list = ['foo', 'bar'].filter(x => x.startsWith('a'))
    const result = last(list)
    result // $ExpectType string | undefined
  })
})

Rambda is fastest. Ramda is 93.43% slower and Lodash is 5.28% slower

const R = require('../../dist/rambda.js')

const list = [1, 2, 3, 4]

const last = [
  {
    label: 'Rambda',
    fn: () => {
      R.last(list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.last(list)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.last(list)
    },
  },
]

lastIndexOf

lastIndexOf<T>(target: T, list: T[]): number

It returns the last index of target in list array.

R.equals is used to determine equality between target and members of list.

If there is no such index, then -1 is returned.

const list = [1, 2, 3, 1, 2, 3]
const result = [
  R.lastIndexOf(2, list),
  R.lastIndexOf(4, list),
]
// => [4, -1]

Try this R.lastIndexOf example in Rambda REPL

All Typescript definitions

lastIndexOf<T>(target: T, list: T[]): number;
lastIndexOf<T>(target: T): (list: T[]) => number;

R.lastIndexOf source

import {_lastIndexOf} from './equals'

export function lastIndexOf(valueToFind, list) {
  if (arguments.length === 1) {
    return _list => _lastIndexOf(valueToFind, _list)
  }

  return _lastIndexOf(valueToFind, list)
}

Tests

import {lastIndexOf} from './lastIndexOf'
import {lastIndexOf as lastIndexOfRamda} from 'ramda'
import {compareCombinations} from './_internals/testUtils'
import {possibleTargets, possibleIterables} from './indexOf.spec.js'

test('with NaN', () => {
  expect(lastIndexOf(NaN, [NaN])).toEqual(0)
})

test('will throw with bad input', () => {
  expect(lastIndexOfRamda([], true)).toEqual(-1)
  expect(() => indexOf([], true)).toThrow()
})

test('without list of objects - no R.equals', () => {
  expect(lastIndexOf(3, [1, 2, 3, 4])).toEqual(2)
  expect(lastIndexOf(10)([1, 2, 3, 4])).toEqual(-1)
})

test('list of objects uses R.equals', () => {
  const listOfObjects = [{a: 1}, {b: 2}, {c: 3}]
  expect(lastIndexOf({c: 4}, listOfObjects)).toBe(-1)
  expect(lastIndexOf({c: 3}, listOfObjects)).toBe(2)
})

test('list of arrays uses R.equals', () => {
  const listOfLists = [[1], [2, 3], [2, 3, 4], [2, 3], [1], []]
  expect(lastIndexOf([], listOfLists)).toBe(5)
  expect(lastIndexOf([1], listOfLists)).toBe(4)
  expect(lastIndexOf([2, 3, 4], listOfLists)).toBe(2)
  expect(lastIndexOf([2, 3, 5], listOfLists)).toBe(-1)
})

test('with string as iterable', () => {
  expect(() => lastIndexOf('a', 'abc')).toThrowWithMessage(
    Error,
    `Cannot read property 'indexOf' of abc`
  )
  expect(lastIndexOfRamda('a', 'abc')).toBe(0)
})

describe('brute force', () => {
  compareCombinations({
    fn: lastIndexOf,
    fnRamda: lastIndexOfRamda,
    firstInput: possibleTargets,
    secondInput: possibleIterables,
    callback: errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        Object {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 34,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 51,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 170,
        }
      `)
    },
  })
})

Typescript test

import {lastIndexOf} from 'rambda'

const list = [1, 2, 3]

describe('R.lastIndexOf', () => {
  it('happy', () => {
    const result = lastIndexOf(2, list)
    result // $ExpectType number
  })
  it('curried', () => {
    const result = lastIndexOf(2)(list)
    result // $ExpectType number
  })
})

Rambda is faster than Ramda with 85.19%

const R = require('../../dist/rambda.js')

const isEven = n => n % 2 === 0
const arr = [1, 3, 5, 7, 9, 11]

const lastIndexOf = [
  {
    label: 'Rambda',
    fn: () => {
      R.lastIndexOf(1, [1, 2, 3, 1, 2])
      R.lastIndexOf(1)([1, 2, 3, 1, 2])
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.lastIndexOf(1, [1, 2, 3, 1, 2])
      Ramda.lastIndexOf(1)([1, 2, 3, 1, 2])
    },
  },
]

length

length<T>(input: T[]): number

It returns the length property of list or string input.

const result = [
  R.length([1, 2, 3, 4]),
  R.length('foo'),
]
// => [4, 3]

Try this R.length example in Rambda REPL

All Typescript definitions

length<T>(input: T[]): number;

R.length source

import {_isArray} from './_internals/_isArray'

export function length(x) {
  if (_isArray(x)) return x.length
  if (typeof x === 'string') return x.length

  return NaN
}

Tests

import {length} from './length'
import {length as lengthRamda} from 'ramda'

test('happy', () => {
  expect(length('foo')).toEqual(3)
  expect(length([1, 2, 3])).toEqual(3)
  expect(length([])).toEqual(0)
})

test('with empty string', () => {
  expect(length('')).toEqual(0)
})

test('with bad input returns NaN', () => {
  expect(length(0)).toBeNaN()
  expect(length({})).toBeNaN()
  expect(length(null)).toBeNaN()
  expect(length(undefined)).toBeNaN()
})

test('with length as property', () => {
  const input1 = {length: '123'}
  const input2 = {length: null}
  const input3 = {length: ''}

  expect(length(input1)).toBeNaN()
  expect(lengthRamda(input1)).toBeNaN()
  expect(length(input2)).toBeNaN()
  expect(lengthRamda(input2)).toBeNaN()
  expect(length(input3)).toBeNaN()
  expect(lengthRamda(input3)).toBeNaN()
})

lens

lens<T, U, V>(getter: (s: T) => U, setter: (a: U, s: T) => V): Lens

It returns a lens for the given getter and setter functions.

The getter gets the value of the focus; the setter sets the value of the focus.

The setter should not mutate the data structure.

const xLens = R.lens(R.prop('x'), R.assoc('x'));

R.view(xLens, {x: 1, y: 2}) // => 1
R.set(xLens, 4, {x: 1, y: 2}) // => {x: 4, y: 2}
R.over(xLens, R.negate, {x: 1, y: 2}) // => {x: -1, y: 2}

Try this R.lens example in Rambda REPL

All Typescript definitions

lens<T, U, V>(getter: (s: T) => U, setter: (a: U, s: T) => V): Lens;

R.lens source

export function lens(getter, setter) {
  return function (functor) {
    return function (target) {
      return functor(getter(target)).map(focus => setter(focus, target))
    }
  }
}

Typescript test

import {lens, assoc} from 'rambda'

interface Input {
  foo: string
}

describe('R.lens', () => {
  it('happy', () => {
    const fn = lens<Input, string, string>((x: Input) => {
      x.foo // $ExpectType string
      return x.foo
    }, assoc('name'))
    fn // $ExpectType Lens
  })
})

lensIndex

lensIndex(index: number): Lens

It returns a lens that focuses on specified index.

const list = ['a', 'b', 'c']
const headLens = R.lensIndex(0)

R.view(headLens, list) // => 'a'
R.set(headLens, 'x', list) // => ['x', 'b', 'c']
R.over(headLens, R.toUpper, list) // => ['A', 'b', 'c']

Try this R.lensIndex example in Rambda REPL

All Typescript definitions

lensIndex(index: number): Lens;

R.lensIndex source

import {lens} from './lens'
import {nth} from './nth'
import {update} from './update'

export function lensIndex(index) {
  return lens(nth(index), update(index))
}

Tests

import {compose} from './compose'
import {keys} from './keys'
import {lensIndex} from './lensIndex'
import {over} from './over'
import {set} from './set'
import {view} from './view'

const testList = [{a: 1}, {b: 2}, {c: 3}]

test('focuses list element at the specified index', () => {
  expect(view(lensIndex(0), testList)).toEqual({a: 1})
})

test('returns undefined if the specified index does not exist', () => {
  expect(view(lensIndex(10), testList)).toEqual(undefined)
})

test('sets the list value at the specified index', () => {
  expect(set(lensIndex(0), 0, testList)).toEqual([0, {b: 2}, {c: 3}])
})

test('applies function to the value at the specified list index', () => {
  expect(over(lensIndex(2), keys, testList)).toEqual([{a: 1}, {b: 2}, ['c']])
})

test('can be composed', () => {
  const nestedList = [0, [10, 11, 12], 1, 2]
  const composedLens = compose(lensIndex(1), lensIndex(0))

  expect(view(composedLens, nestedList)).toEqual(10)
})

test('set s (get s) === s', () => {
  expect(set(lensIndex(0), view(lensIndex(0), testList), testList)).toEqual(
    testList
  )
})

test('get (set s v) === v', () => {
  expect(view(lensIndex(0), set(lensIndex(0), 0, testList))).toEqual(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(
    view(
      lensIndex(0),
      set(lensIndex(0), 11, set(lensIndex(0), 10, testList))
    )
  ).toEqual(11)
})

Typescript test

import {view, lensIndex} from 'rambda'

interface Input {
  a: number
}
const testList: Input[] = [{a: 1}, {a: 2}, {a: 3}]

describe('R.lensIndex', () => {
  it('happy', () => {
    const result = view<Input[], Input>(lensIndex(0), testList)
    result // $ExpectType Input
    result.a // $ExpectType number
  })
})

lensPath

lensPath(path: RamdaPath): Lens

It returns a lens that focuses on specified path.

const lensPath = R.lensPath(['x', 0, 'y'])
const input = {x: [{y: 2, z: 3}, {y: 4, z: 5}]}

R.view(lensPath, input) // => 2

R.set(lensPath, 1, input) 
// => {x: [{y: 1, z: 3}, {y: 4, z: 5}]}

R.over(xHeadYLens, R.negate, input) 
// => {x: [{y: -2, z: 3}, {y: 4, z: 5}]}

Try this R.lensPath example in Rambda REPL

All Typescript definitions

lensPath(path: RamdaPath): Lens;
lensPath(path: string): Lens;

R.lensPath source

import {assocPath} from './assocPath'
import {lens} from './lens'
import {path} from './path'

export function lensPath(key) {
  return lens(path(key), assocPath(key))
}

Tests

import {compose} from './compose'
import {identity} from './identity'
import {inc} from './inc'
import {lensPath} from './lensPath'
import {lensProp} from './lensProp'
import {over} from './over'
import {set} from './set'
import {view} from './view'

const testObj = {
  a: [{b: 1}, {b: 2}],
  d: 3,
}

test('view', () => {
  expect(view(lensPath('d'), testObj)).toEqual(3)
  expect(view(lensPath('a.0.b'), testObj)).toEqual(1)
  // this is different to ramda, as ramda will return a clone of the input object
  expect(view(lensPath(''), testObj)).toEqual(undefined)
})

test('set', () => {
  expect(set(lensProp('d'), 0, testObj)).toEqual({
    a: [{b: 1}, {b: 2}],
    d: 0,
  })
  expect(set(lensPath('a.0.b'), 0, testObj)).toEqual({
    a: [{b: 0}, {b: 2}],
    d: 3,
  })
  expect(set(lensPath('a.0.X'), 0, testObj)).toEqual({
    a: [
      {
        b: 1,
        X: 0,
      },
      {b: 2},
    ],
    d: 3,
  })
  expect(set(lensPath([]), 0, testObj)).toEqual(0)
})

test('over', () => {
  expect(over(lensPath('d'), inc, testObj)).toEqual({
    a: [{b: 1}, {b: 2}],
    d: 4,
  })
  expect(over(lensPath('a.1.b'), inc, testObj)).toEqual({
    a: [{b: 1}, {b: 3}],
    d: 3,
  })
  expect(over(lensProp('X'), identity, testObj)).toEqual({
    a: [{b: 1}, {b: 2}],
    d: 3,
    X: undefined,
  })
  expect(over(lensPath('a.0.X'), identity, testObj)).toEqual({
    a: [
      {
        b: 1,
        X: undefined,
      },
      {b: 2},
    ],
    d: 3,
  })
})

test('compose', () => {
  const composedLens = compose(lensPath('a'), lensPath('1.b'))
  expect(view(composedLens, testObj)).toEqual(2)
})

test('set s (get s) === s', () => {
  expect(
    set(lensPath(['d']), view(lensPath(['d']), testObj), testObj)
  ).toEqual(testObj)
  expect(
    set(
      lensPath(['a', 0, 'b']),
      view(lensPath(['a', 0, 'b']), testObj),
      testObj
    )
  ).toEqual(testObj)
})

test('get (set s v) === v', () => {
  expect(view(lensPath(['d']), set(lensPath(['d']), 0, testObj))).toEqual(0)
  expect(
    view(lensPath(['a', 0, 'b']), set(lensPath(['a', 0, 'b']), 0, testObj))
  ).toEqual(0)
})

test('get (set(set s v1) v2) === v2', () => {
  const p = ['d']
  const q = ['a', 0, 'b']
  expect(
    view(lensPath(p), set(lensPath(p), 11, set(lensPath(p), 10, testObj)))
  ).toEqual(11)
  expect(
    view(lensPath(q), set(lensPath(q), 11, set(lensPath(q), 10, testObj)))
  ).toEqual(11)
})

Typescript test

import {lensPath, view} from 'rambda'

interface Input {
  foo: number[]
  bar: {
    a: string
    b: string
  }
}

const testObject: Input = {
  foo: [1, 2],
  bar: {
    a: 'x',
    b: 'y',
  },
}

const path = lensPath(['bar', 'a'])
const pathAsString = lensPath('bar.a')

describe('R.lensPath', () => {
  it('happy', () => {
    const result = view<Input, string>(path, testObject)
    result // $ExpectType string
  })
  it('using string as path input', () => {
    const result = view<Input, string>(pathAsString, testObject)
    result // $ExpectType string
  })
})

lensProp

lensProp(prop: string): {
  <T, U>(obj: T): U

It returns a lens that focuses on specified property prop.

const xLens = R.lensProp('x');
const input = {x: 1, y: 2}

R.view(xLens, input) // => 1

R.set(xLens, 4, input) 
// => {x: 4, y: 2}

R.over(xLens, R.negate, input) 
// => {x: -1, y: 2}

Try this R.lensProp example in Rambda REPL

All Typescript definitions

lensProp(prop: string): {
  <T, U>(obj: T): U;
  set<T, U, V>(val: T, obj: U): V;
};

R.lensProp source

import {assoc} from './assoc'
import {lens} from './lens'
import {prop} from './prop'

export function lensProp(key) {
  return lens(prop(key), assoc(key))
}

Tests

import {compose} from './compose'
import {identity} from './identity'
import {inc} from './inc'
import {lensProp} from './lensProp'
import {over} from './over'
import {set} from './set'
import {view} from './view'

const testObj = {
  a: 1,
  b: 2,
  c: 3,
}

test('focuses object the specified object property', () => {
  expect(view(lensProp('a'), testObj)).toEqual(1)
})

test('returns undefined if the specified property does not exist', () => {
  expect(view(lensProp('X'), testObj)).toEqual(undefined)
})

test('sets the value of the object property specified', () => {
  expect(set(lensProp('a'), 0, testObj)).toEqual({
    a: 0,
    b: 2,
    c: 3,
  })
})

test("adds the property to the object if it doesn't exist", () => {
  expect(set(lensProp('d'), 4, testObj)).toEqual({
    a: 1,
    b: 2,
    c: 3,
    d: 4,
  })
})

test('applies function to the value of the specified object property', () => {
  expect(over(lensProp('a'), inc, testObj)).toEqual({
    a: 2,
    b: 2,
    c: 3,
  })
})

test("applies function to undefined and adds the property if it doesn't exist", () => {
  expect(over(lensProp('X'), identity, testObj)).toEqual({
    a: 1,
    b: 2,
    c: 3,
    X: undefined,
  })
})

test('can be composed', () => {
  const nestedObj = {
    a: {b: 1},
    c: 2,
  }
  const composedLens = compose(lensProp('a'), lensProp('b'))

  expect(view(composedLens, nestedObj)).toEqual(1)
})

test('set s (get s) === s', () => {
  expect(set(lensProp('a'), view(lensProp('a'), testObj), testObj)).toEqual(
    testObj
  )
})

test('get (set s v) === v', () => {
  expect(view(lensProp('a'), set(lensProp('a'), 0, testObj))).toEqual(0)
})

test('get (set(set s v1) v2) === v2', () => {
  expect(
    view(
      lensProp('a'),
      set(lensProp('a'), 11, set(lensProp('a'), 10, testObj))
    )
  ).toEqual(11)
})

Typescript test

import {lensProp, view} from 'rambda'

interface Input {
  foo: string
}

const testObject: Input = {
  foo: 'Led Zeppelin',
}

const lens = lensProp('foo')

describe('R.lensProp', () => {
  it('happy', () => {
    const result = view<Input, string>(lens, testObject)
    result // $ExpectType string
  })
})

map

map<T, U>(fn: ObjectIterator<T, U>, iterable: Dictionary<T>): Dictionary<U>

It returns the result of looping through iterable with fn.

It works with both array and object.

💥 Unlike Ramda's map, here property and input object are passed as arguments to fn, when iterable is an object.

const fn = x => x * 2
const fnWhenObject = (val, prop)=>{
  return `${prop}-${val}`
}

const iterable = [1, 2]
const obj = {a: 1, b: 2}

const result = [ 
  R.map(fn, list),
  R.map(fnWhenObject, obj)
]
// => [ [1, 4], {a: 'a-1', b: 'b-2'}]

Try this R.map example in Rambda REPL

All Typescript definitions

map<T, U>(fn: ObjectIterator<T, U>, iterable: Dictionary<T>): Dictionary<U>;
map<T, U>(fn: Iterator<T, U>, iterable: T[]): U[];
map<T, U>(fn: Iterator<T, U>): (iterable: T[]) => U[];
map<T, U, S>(fn: ObjectIterator<T, U>): (iterable: Dictionary<T>) => Dictionary<U>;
map<T>(fn: Iterator<T, T>): (iterable: T[]) => T[];
map<T>(fn: Iterator<T, T>, iterable: T[]): T[];

R.map source

import {_isArray} from './_internals/_isArray'
import {_keys} from './_internals/_keys'

export function mapArray(fn, list, isIndexed = false) {
  let index = 0
  const willReturn = Array(list.length)

  while (index < list.length) {
    willReturn[index] = isIndexed ? fn(list[index], index) : fn(list[index])

    index++
  }

  return willReturn
}

export function mapObject(fn, obj) {
  let index = 0
  const keys = _keys(obj)
  const len = keys.length
  const willReturn = {}

  while (index < len) {
    const key = keys[index]
    willReturn[key] = fn(obj[key], key, obj)
    index++
  }

  return willReturn
}

export const mapObjIndexed = mapObject

export function map(fn, iterable) {
  if (arguments.length === 1) return _iterable => map(fn, _iterable)
  if (!iterable) {
    throw new Error('Incorrect iterable input')
  }

  if (_isArray(iterable)) return mapArray(fn, iterable)

  return mapObject(fn, iterable)
}

Tests

import {map} from './map'
import {map as mapRamda} from 'ramda'

const double = x => x * 2

describe(`with array`, () => {
  test('happy', () => {
    expect(map(double, [1, 2, 3])).toEqual([2, 4, 6])
  })

  test('curried', () => {
    expect(map(double)([1, 2, 3])).toEqual([2, 4, 6])
  })
})

describe(`with object`, () => {
  const obj = {
    a: 1,
    b: 2,
  }

  test('happy', () => {
    expect(map(double, obj)).toEqual({
      a: 2,
      b: 4,
    })
  })
  test('property as second and input object as third argument', () => {
    const obj = {
      a: 1,
      b: 2,
    }
    const iterator = (val, prop, inputObject) => {
      expect(prop).toBeString()
      expect(inputObject).toEqual(obj)

      return val * 2
    }

    expect(map(iterator)(obj)).toEqual({
      a: 2,
      b: 4,
    })
  })
})

test('bad inputs difference between Ramda and Rambda', () => {
  expect(() => map(double, null)).toThrowWithMessage(
    Error,
    `Incorrect iterable input`
  )
  expect(() => map(double)(undefined)).toThrowWithMessage(
    Error,
    `Incorrect iterable input`
  )
  expect(() => mapRamda(double, null)).toThrowWithMessage(
    TypeError,
    `Cannot read properties of null (reading 'fantasy-land/map')`
  )
  expect(() => mapRamda(double, undefined)).toThrowWithMessage(
    TypeError,
    `Cannot read properties of undefined (reading 'fantasy-land/map')`
  )
})

Typescript test

import {map} from 'rambda'

describe('R.map with arrays', () => {
  it('iterable returns the same type as the input', () => {
    const result = map<number>(
      (x: number) => {
        x // $ExpectType number
        return x + 2
      },
      [1, 2, 3]
    )
    result // $ExpectType number[]
  })
  it('iterable returns the same type as the input - curried', () => {
    const result = map<number>((x: number) => {
      x // $ExpectType number
      return x + 2
    })([1, 2, 3])
    result // $ExpectType number[]
  })
  it('iterable returns different type as the input', () => {
    const result = map<number, string>(
      (x: number) => {
        x // $ExpectType number
        return String(x)
      },
      [1, 2, 3]
    )
    result // $ExpectType string[]
  })
})

describe('R.map with objects', () => {
  it('iterable with all three arguments - curried', () => {
    // It requires dummy third typing argument
    // in order to identify compared to curry typings for arrays
    // ============================================
    const result = map<number, string, any>((a, b, c) => {
      a // $ExpectType number
      b // $ExpectType string
      c // $ExpectType Dictionary<number>
      return `${a}`
    })({a: 1, b: 2})
    result // $ExpectType Dictionary<string>
  })
  it('iterable with all three arguments', () => {
    const result = map<number, string>(
      (a, b, c) => {
        a // $ExpectType number
        b // $ExpectType string
        c // $ExpectType Dictionary<number>
        return `${a}`
      },
      {a: 1, b: 2}
    )
    result // $ExpectType Dictionary<string>
  })
  it('iterable with property argument', () => {
    const result = map<number, string>(
      (a, b) => {
        a // $ExpectType number
        b // $ExpectType string
        return `${a}`
      },
      {a: 1, b: 2}
    )
    result // $ExpectType Dictionary<string>
  })
  it('iterable with no property argument', () => {
    const result = map<number, string>(
      a => {
        a // $ExpectType number
        return `${a}`
      },
      {a: 1, b: 2}
    )
    result // $ExpectType Dictionary<string>
  })
})

Rambda is fastest. Ramda is 86.6% slower and Lodash is 11.73% slower

const R = require('../../dist/rambda.js')

const arr = [1, 2, 3, 4]
const fn = x => x * 2
const map = [
  {
    label: 'Rambda',
    fn: () => {
      R.map(fn, arr)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.map(fn, arr)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.map(arr, fn)
    },
  },
]

mapObjIndexed

It works the same way as R.map does for objects. It is added as Ramda also has this method.

const fn = (val, prop) => {
  return `${prop}-${val}`
}

const obj = {a: 1, b: 2}

const result = R.map(mapObjIndexed, obj)
// => {a: 'a-1', b: 'b-2'}

Try this R.mapObjIndexed example in Rambda REPL

match

match(regExpression: RegExp, str: string): string[]

Curried version of String.prototype.match which returns empty array, when there is no match.

const result = [
  R.match('a', 'foo'),
  R.match(/([a-z]a)/g, 'bananas')
]
// => [[], ['ba', 'na', 'na']]

Try this R.match example in Rambda REPL

All Typescript definitions

match(regExpression: RegExp, str: string): string[];
match(regExpression: RegExp): (str: string) => string[];

R.match source

export function match(pattern, input) {
  if (arguments.length === 1) return _input => match(pattern, _input)

  const willReturn = input.match(pattern)

  return willReturn === null ? [] : willReturn
}

Tests

import {equals} from './equals'
import {match} from './match'

test('happy', () => {
  expect(match(/a./g)('foo bar baz')).toEqual(['ar', 'az'])
})

test('fallback', () => {
  expect(match(/a./g)('foo')).toEqual([])
})

test('with string', () => {
  expect(match('a', 'foo')).toEqual([])
  expect(equals(match('o', 'foo'), ['o'])).toBeTrue()
})

test('throwing', () => {
  expect(() => {
    match(/a./g, null)
  }).toThrowWithMessage(
    TypeError,
    `Cannot read properties of null (reading 'match')`
  )
})

Typescript test

import {match} from 'rambda'

const str = 'foo bar'

describe('R.match', () => {
  it('happy', () => {
    const result = match(/foo/, str)
    result // $ExpectType string[]
  })
  it('curried', () => {
    const result = match(/foo/)(str)
    result // $ExpectType string[]
  })
})

Rambda is faster than Ramda with 44.83%

const R = require('../../dist/rambda.js')

const match = [
  {
    label: 'Rambda',
    fn: () => {
      R.match(/a./g)('foo bar baz')
      R.match(/a./g, 'foo bar baz')
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.match(/a./g)('foo bar baz')
      Ramda.match(/a./g, 'foo bar baz')
    },
  },
]

mathMod

R.mathMod behaves like the modulo operator should mathematically, unlike the % operator (and by extension, R.modulo). So while -17 % 5 is -2, mathMod(-17, 5) is 3.

💥 Explanation is taken from Ramda documentation site.

const result = [
  R.mathMod(-17, 5),
  R.mathMod(17, 5),
  R.mathMod(17, -5),  
  R.mathMod(17, 0)   
]
// => [3, 2, NaN, NaN]

Try this R.mathMod example in Rambda REPL

max

It returns the greater value between x and y.

const result = [
  R.max(5, 7),  
  R.max('bar', 'foo'),  
]
// => [7, 'foo']

Try this R.max example in Rambda REPL

maxBy

It returns the greater value between x and y according to compareFn function.

const compareFn = Math.abs

R.maxBy(compareFn, 5, -7) // => -7

Try this R.maxBy example in Rambda REPL

mean

mean(list: number[]): number

It returns the mean value of list input.

R.mean([ 2, 7 ])
// => 4.5

Try this R.mean example in Rambda REPL

All Typescript definitions

mean(list: number[]): number;

R.mean source

import {sum} from './sum'

export function mean(list) {
  return sum(list) / list.length
}

Tests

import {mean} from './mean'

test('happy', () => {
  expect(mean([2, 7])).toBe(4.5)
})

test('with NaN', () => {
  expect(mean([])).toBeNaN()
})

Typescript test

import {mean} from 'rambda'

describe('R.mean', () => {
  it('happy', () => {
    const result = mean([1, 2, 3])

    result // $ExpectType number
  })
})

median

median(list: number[]): number

It returns the median value of list input.

R.median([ 7, 2, 10, 9 ]) // => 8

Try this R.median example in Rambda REPL

All Typescript definitions

median(list: number[]): number;

R.median source

import {mean} from './mean'

export function median(list) {
  const len = list.length
  if (len === 0) return NaN
  const width = 2 - (len % 2)
  const idx = (len - width) / 2

  return mean(
    Array.prototype.slice
      .call(list, 0)
      .sort((a, b) => {
        if (a === b) return 0

        return a < b ? -1 : 1
      })
      .slice(idx, idx + width)
  )
}

Tests

import {median} from './median'

test('happy', () => {
  expect(median([2])).toEqual(2)
  expect(median([7, 2, 10, 2, 9])).toEqual(7)
})

test('with empty array', () => {
  expect(median([])).toBeNaN()
})

Typescript test

import {median} from 'rambda'

describe('R.median', () => {
  it('happy', () => {
    const result = median([1, 2, 3])

    result // $ExpectType number
  })
})

merge

merge<A, B>(target: A, newProps: B): A & B
export function merge<Output>(target: any): (newProps: any) => Output

It creates a copy of target object with overidden newProps properties.

const target = { 'foo': 0, 'bar': 1 }
const newProps = { 'foo': 7 }

const result = R.merge(target, newProps)
// => { 'foo': 7, 'bar': 1 }

Try this R.merge example in Rambda REPL

All Typescript definitions

merge<A, B>(target: A, newProps: B): A & B
merge<Output>(target: any): (newProps: any) => Output;

R.merge source

export function merge(target, newProps) {
  if (arguments.length === 1) return _newProps => merge(target, _newProps)

  return Object.assign({}, target || {}, newProps || {})
}

Tests

import {merge} from './merge'

const obj = {
  foo: 1,
  bar: 2,
}

test('happy', () => {
  expect(merge(obj, {bar: 20})).toEqual({
    foo: 1,
    bar: 20,
  })
})

test('curry', () => {
  expect(merge(obj)({baz: 3})).toEqual({
    foo: 1,
    bar: 2,
    baz: 3,
  })
})

/**
 * https://github.com/selfrefactor/rambda/issues/77
 */
test('when undefined or null instead of object', () => {
  expect(merge(null, undefined)).toEqual({})
  expect(merge(obj, null)).toEqual(obj)
  expect(merge(obj, undefined)).toEqual(obj)
  expect(merge(undefined, obj)).toEqual(obj)
})

Typescript test

import {merge} from 'rambda'

interface Output {
  foo: number
  bar: number
}

describe('R.merge', () => {
  const result = merge({foo: 1}, {bar: 2})
  const curriedResult = merge<Output>({foo: 1})({bar: 2})

  result.foo // $ExpectType number
  result.bar // $ExpectType number
  curriedResult.bar // $ExpectType number
})

Rambda is fastest. Ramda is 12.21% slower and Lodash is 55.76% slower

const R = require('../../dist/rambda.js')

const obj = {bar: 'yes'}
const a = {
  foo: 'bar',
  bar: 'baz',
}
const merge = [
  {
    label: 'Rambda',
    fn: () => {
      R.merge(a, obj)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.merge(a, obj)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.merge(a, obj)
    },
  },
]

mergeAll

mergeAll<T>(list: object[]): T

It merges all objects of list array sequentially and returns the result.

const list = [
  {a: 1},
  {b: 2},
  {c: 3}
]
const result = R.mergeAll(list)
const expected = {
  a: 1,
  b: 2,
  c: 3
}
// => `result` is equal to `expected`

Try this R.mergeAll example in Rambda REPL

All Typescript definitions

mergeAll<T>(list: object[]): T;
mergeAll(list: object[]): object;

R.mergeAll source

import {map} from './map'
import {merge} from './merge'

export function mergeAll(arr) {
  let willReturn = {}
  map(val => {
    willReturn = merge(willReturn, val)
  }, arr)

  return willReturn
}

Tests

import {mergeAll} from './mergeAll'

test('case 1', () => {
  const arr = [{a: 1}, {b: 2}, {c: 3}]
  const expectedResult = {
    a: 1,
    b: 2,
    c: 3,
  }
  expect(mergeAll(arr)).toEqual(expectedResult)
})

test('case 2', () => {
  expect(mergeAll([{foo: 1}, {bar: 2}, {baz: 3}])).toEqual({
    foo: 1,
    bar: 2,
    baz: 3,
  })
})

Typescript test

import {mergeAll} from 'rambda'

describe('R.mergeAll', () => {
  it('with passing type', () => {
    interface Output {
      foo: number
      bar: number
    }
    const result = mergeAll<Output>([{foo: 1}, {bar: 2}])
    result.foo // $ExpectType number
    result.bar // $ExpectType number
  })

  it('without passing type', () => {
    const result = mergeAll([{foo: 1}, {bar: 2}])
    result // $ExpectType unknown
  })
})

mergeDeepRight

mergeDeepRight<Output>(target: object, newProps: object): Output

Creates a new object with the own properties of the first object merged with the own properties of the second object. If a key exists in both objects:

and both values are objects, the two values will be recursively merged
otherwise the value from the second object will be used.

All Typescript definitions

mergeDeepRight<Output>(target: object, newProps: object): Output;
mergeDeepRight<Output>(target: object): (newProps: object) => Output;

R.mergeDeepRight source

import {type} from './type'

export function mergeDeepRight(target, source) {
  if (arguments.length === 1) {
    return sourceHolder => mergeDeepRight(target, sourceHolder)
  }

  const willReturn = JSON.parse(JSON.stringify(target))

  Object.keys(source).forEach(key => {
    if (type(source[key]) === 'Object') {
      if (type(target[key]) === 'Object') {
        willReturn[key] = mergeDeepRight(target[key], source[key])
      } else {
        willReturn[key] = source[key]
      }
    } else {
      willReturn[key] = source[key]
    }
  })

  return willReturn
}

Tests

// import { mergeDeepRight } from 'ramda'
import {mergeDeepRight} from './mergeDeepRight'

const slave = {
  name: 'evilMe',
  age: 10,
  contact: {
    a: 1,
    email: 'foo@example.com',
  },
}
const master = {
  age: 40,
  contact: {email: 'baz@example.com'},
  songs: {title: 'Remains the same'},
}

test('happy', () => {
  const result = mergeDeepRight(slave, master)
  const curryResult = mergeDeepRight(slave)(master)
  const expected = {
    age: 40,
    name: 'evilMe',
    contact: {
      a: 1,
      email: 'baz@example.com',
    },
    songs: {title: 'Remains the same'},
  }

  expect(result).toEqual(expected)
  expect(curryResult).toEqual(expected)
})

test('ramda compatible test 1', () => {
  const a = {
    w: 1,
    x: 2,
    y: {z: 3},
  }
  const b = {
    a: 4,
    b: 5,
    c: {d: 6},
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    w: 1,
    x: 2,
    y: {z: 3},
    a: 4,
    b: 5,
    c: {d: 6},
  }

  expect(result).toEqual(expected)
})

test('ramda compatible test 2', () => {
  const a = {
    a: {
      b: 1,
      c: 2,
    },
    y: 0,
  }
  const b = {
    a: {
      b: 3,
      d: 4,
    },
    z: 0,
  }
  const result = mergeDeepRight(a, b)
  const expected = {
    a: {
      b: 3,
      c: 2,
      d: 4,
    },
    y: 0,
    z: 0,
  }

  expect(result).toEqual(expected)
})

test('ramda compatible test 3', () => {
  const a = {
    w: 1,
    x: {y: 2},
  }
  const result = mergeDeepRight(a, {x: {y: 3}})
  const expected = {
    w: 1,
    x: {y: 3},
  }
  expect(result).toEqual(expected)
})

Typescript test

import {mergeDeepRight} from 'rambda'

interface Output {
  foo: {
    bar: number
  }
}

describe('R.mergeDeepRight', () => {
  const result = mergeDeepRight<Output>({foo: {bar: 1}}, {foo: {bar: 2}})
  result.foo.bar // $ExpectType number
})

mergeLeft

mergeLeft<Output>(newProps: object, target: object): Output

Same as R.merge, but in opposite direction.

const result = R.mergeLeft(
  {a: 10},
  {a: 1, b: 2}
)
// => {a:10, b: 2}

Try this R.mergeLeft example in Rambda REPL

All Typescript definitions

mergeLeft<Output>(newProps: object, target: object): Output;
mergeLeft<Output>(newProps: object): (target: object) => Output;

R.mergeLeft source

import {merge} from './merge'

export function mergeLeft(x, y) {
  if (arguments.length === 1) return _y => mergeLeft(x, _y)

  return merge(y, x)
}

Tests

import {mergeLeft} from './mergeLeft'

const obj = {
  foo: 1,
  bar: 2,
}

test('happy', () => {
  expect(mergeLeft({bar: 20}, obj)).toEqual({
    foo: 1,
    bar: 20,
  })
})

test('curry', () => {
  expect(mergeLeft({baz: 3})(obj)).toEqual({
    foo: 1,
    bar: 2,
    baz: 3,
  })
})

test('when undefined or null instead of object', () => {
  expect(mergeLeft(null, undefined)).toEqual({})
  expect(mergeLeft(obj, null)).toEqual(obj)
  expect(mergeLeft(obj, undefined)).toEqual(obj)
  expect(mergeLeft(undefined, obj)).toEqual(obj)
})

Typescript test

import {mergeLeft} from 'rambda'

interface Output {
  foo: number
  bar: number
}

describe('R.mergeLeft', () => {
  const result = mergeLeft<Output>({foo: 1}, {bar: 2})
  const curriedResult = mergeLeft<Output>({foo: 1})({bar: 2})

  result.foo // $ExpectType number
  result.bar // $ExpectType number
  curriedResult.bar // $ExpectType number
})

min

It returns the lesser value between x and y.

const result = [
  R.min(5, 7),  
  R.min('bar', 'foo'),  
]
// => [5, 'bar']

Try this R.min example in Rambda REPL

minBy

It returns the lesser value between x and y according to compareFn function.

const compareFn = Math.abs

R.minBy(compareFn, -5, 2) // => -5

Try this R.minBy example in Rambda REPL

modulo

Curried version of x%y.

R.modulo(17, 3) // => 2

Try this R.modulo example in Rambda REPL

move

It returns a copy of list with exchanged fromIndex and toIndex elements.

💥 Rambda.move doesn't support negative indexes - it throws an error.

const list = [1, 2, 3]
const result = R.move(0, 1, list)
// => [2, 1, 3]

Try this R.move example in Rambda REPL

multiply

Curried version of x*y.

R.multiply(2, 4) // => 8

Try this R.multiply example in Rambda REPL

negate

R.negate(420)// => -420

Try this R.negate example in Rambda REPL

none

none<T>(predicate: (x: T) => boolean, list: T[]): boolean

It returns true, if all members of array list returns false, when applied as argument to predicate function.

const list = [ 0, 1, 2, 3, 4 ]
const predicate = x => x > 6

const result = R.none(predicate, arr)
// => true

Try this R.none example in Rambda REPL

All Typescript definitions

none<T>(predicate: (x: T) => boolean, list: T[]): boolean;
none<T>(predicate: (x: T) => boolean): (list: T[]) => boolean;

R.none source

export function none(predicate, list) {
  if (arguments.length === 1) return _list => none(predicate, _list)

  for (let i = 0; i < list.length; i++) {
    if (!predicate(list[i])) return true
  }

  return false
}

Tests

import {none} from './none'

const isEven = n => n % 2 === 0
const isOdd = n => n % 2 === 1
const arr = [1, 3, 5, 7, 9, 11]

test('when true', () => {
  expect(none(isEven, arr)).toBeTrue()
})

test('when false curried', () => {
  expect(none(isOdd)(arr)).toBeFalse()
})

Typescript test

import {none} from 'rambda'

describe('R.none', () => {
  it('happy', () => {
    const result = none(
      x => {
        x // $ExpectType number
        return x > 0
      },
      [1, 2, 3]
    )
    result // $ExpectType boolean
  })
  it('curried needs a type', () => {
    const result = none<number>(x => {
      x // $ExpectType number
      return x > 0
    })([1, 2, 3])
    result // $ExpectType boolean
  })
})

Rambda is faster than Ramda with 96.48%

const R = require('../../dist/rambda.js')

const isEven = n => n % 2 === 0
const arr = [1, 3, 5, 7, 9, 11]

const none = [
  {
    label: 'Rambda',
    fn: () => {
      R.none(isEven, arr)
      R.none(isEven)(arr)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.none(isEven, arr)
      Ramda.none(isEven)(arr)
    },
  },
]

not

not(input: any): boolean

It returns a boolean negated version of input.

R.not(false) // true

Try this R.not example in Rambda REPL

All Typescript definitions

not(input: any): boolean;

R.not source

export function not(input) {
  return !input
}

Tests

import {not} from './not'

test('not', () => {
  expect(not(false)).toEqual(true)
  expect(not(true)).toEqual(false)
  expect(not(0)).toEqual(true)
  expect(not(1)).toEqual(false)
})

Typescript test

import {not} from 'rambda'

describe('R.not', () => {
  it('happy', () => {
    const result = not(4)

    result // $ExpectType boolean
  })
})

nth

nth<T>(index: number, list: T[]): T | undefined

Curried version of list[index].

const list = [1, 2, 3]
const str = 'foo'

const result = [
  R.nth(2, list),
  R.nth(6, list),
  R.nth(0, str),
]
// => [3, undefined, 'f']

Try this R.nth example in Rambda REPL

All Typescript definitions

nth<T>(index: number, list: T[]): T | undefined;	
nth(index: number): <T>(list: T[]) => T | undefined;

R.nth source

export function nth(index, list) {
  if (arguments.length === 1) return _list => nth(index, _list)

  const idx = index < 0 ? list.length + index : index

  return Object.prototype.toString.call(list) === '[object String]'
    ? list.charAt(idx)
    : list[idx]
}

Tests

import {nth} from './nth'

test('happy', () => {
  expect(nth(2, [1, 2, 3, 4])).toEqual(3)
})

test('with curry', () => {
  expect(nth(2)([1, 2, 3, 4])).toEqual(3)
})

test('with string', () => {
  expect(nth(2)('foo')).toEqual('o')
})

test('with negative index', () => {
  expect(nth(-3)([1, 2, 3, 4])).toEqual(2)
})

Typescript test

import {nth} from 'rambda'

const list = [1, 2, 3]

describe('R.nth', () => {
  it('happy', () => {
    const result = nth(4, list)

    result // $ExpectType number | undefined
  })
  it('curried', () => {
    const result = nth(1)(list)

    result // $ExpectType number | undefined
  })
})

objOf

It creates an object with a single key-value pair.

const result = R.objOf('foo', 'bar')
// => {foo: 'bar'}

Try this R.objOf example in Rambda REPL

of

of<T>(x: T): T[]

R.of(null); // => [null]
R.of([42]); // => [[42]]

Try this R.of example in Rambda REPL

All Typescript definitions

of<T>(x: T): T[];

R.of source

export function of(value) {
  return [value]
}

Tests

import {of} from './of'

test('happy', () => {
  expect(of(3)).toEqual([3])

  expect(of(null)).toEqual([null])
})

Typescript test

import {of} from 'ramda'

const list = [1, 2, 3]

describe('R.of', () => {
  it('happy', () => {
    const result = of(4)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = of(list)

    result // $ExpectType number[][]
  })
})

omit

omit<T, K extends string>(propsToOmit: K[], obj: T): Omit<T, K>

It returns a partial copy of an obj without propsToOmit properties.

💥 When using this method with TypeScript, it is much easier to pass propsToOmit as an array. If passing a string, you will need to explicitly declare the output type.

const obj = {a: 1, b: 2, c: 3}
const propsToOmit = 'a,c,d'
const propsToOmitList = ['a', 'c', 'd']

const result = [
  R.omit(propsToOmit, obj), 
  R.omit(propsToOmitList, obj) 
]
// => [{b: 2}, {b: 2}]

Try this R.omit example in Rambda REPL

All Typescript definitions

omit<T, K extends string>(propsToOmit: K[], obj: T): Omit<T, K>;
omit<K extends string>(propsToOmit: K[]): <T>(obj: T) => Omit<T, K>;
omit<T, U>(propsToOmit: string, obj: T): U;
omit<T, U>(propsToOmit: string): (obj: T) => U;
omit<T>(propsToOmit: string, obj: object): T;
omit<T>(propsToOmit: string): (obj: object) => T;

R.omit source

export function omit(propsToOmit, obj) {
  if (arguments.length === 1) return _obj => omit(propsToOmit, _obj)

  if (obj === null || obj === undefined) {
    return undefined
  }

  const propsToOmitValue =
    typeof propsToOmit === 'string' ? propsToOmit.split(',') : propsToOmit

  const willReturn = {}

  for (const key in obj) {
    if (!propsToOmitValue.includes(key)) {
      willReturn[key] = obj[key]
    }
  }

  return willReturn
}

Tests

import {omit} from './omit'

test('with string as condition', () => {
  const obj = {
    a: 1,
    b: 2,
    c: 3,
  }
  const result = omit('a,c', obj)
  const resultCurry = omit('a,c')(obj)
  const expectedResult = {b: 2}

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('with null', () => {
  expect(omit('a,b', null)).toEqual(undefined)
})

test("doesn't work with number as property", () => {
  expect(
    omit([42], {
      a: 1,
      42: 2,
    })
  ).toEqual({
    42: 2,
    a: 1,
  })
})

test('happy', () => {
  expect(
    omit(['a', 'c'])({
      a: 'foo',
      b: 'bar',
      c: 'baz',
    })
  ).toEqual({b: 'bar'})
})

Typescript test

import {omit} from 'rambda'

describe('R.omit with array as props input', () => {
  it('allow Typescript to infer object type', () => {
    const input = {a: 'foo', b: 2, c: 3, d: 4}
    const result = omit(['b,c'], input)

    result.a // $ExpectType string
    result.d // $ExpectType number

    const curriedResult = omit(['a,c'], input)

    curriedResult.a // $ExpectType string
    curriedResult.d // $ExpectType number
  })

  it('declare type of input object', () => {
    interface Input {
      a: string
      b: number
      c: number
      d: number
    }
    const input: Input = {a: 'foo', b: 2, c: 3, d: 4}
    const result = omit(['b,c'], input)
    result // $ExpectType Omit<Input, "b,c">

    result.a // $ExpectType string
    result.d // $ExpectType number

    const curriedResult = omit(['a,c'], input)

    curriedResult.a // $ExpectType string
    curriedResult.d // $ExpectType number
  })
})

describe('R.omit with string as props input', () => {
  interface Output {
    b: number
    d: number
  }

  it('explicitly declare output', () => {
    const result = omit<Output>('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType Output
    result.b // $ExpectType number

    const curriedResult = omit<Output>('a,c')({a: 1, b: 2, c: 3, d: 4})

    curriedResult.b // $ExpectType number
  })

  it('explicitly declare input and output', () => {
    interface Input {
      a: number
      b: number
      c: number
      d: number
    }
    const result = omit<Input, Output>('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType Output
    result.b // $ExpectType number

    const curriedResult = omit<Input, Output>('a,c')({
      a: 1,
      b: 2,
      c: 3,
      d: 4,
    })

    curriedResult.b // $ExpectType number
  })

  it('without passing type', () => {
    const result = omit('a,c', {a: 1, b: 2, c: 3, d: 4})
    result // $ExpectType unknown
  })
})

Rambda is fastest. Ramda is 69.95% slower and Lodash is 97.34% slower

const R = require('../../dist/rambda.js')

const obj = {
  a: 'foo',
  b: 'bar',
  c: 'baz',
}
const toOmit = ['a', 'c']
const omit = [
  {
    label: 'Rambda',
    fn: () => {
      R.omit(toOmit, obj)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.omit(toOmit, obj)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.omit(obj, toOmit)
    },
  },
]

once

once<T extends (...args: any[]) => any>(func: T): T

It returns a function, which invokes only once fn function.

let result = 0
const addOnce = R.once((x) => result = result + x)

addOnce(1)
addOnce(1)
// => 1

Try this R.once example in Rambda REPL

All Typescript definitions

once<T extends (...args: any[]) => any>(func: T): T;

R.once source

import {curry} from './curry'

function onceFn(fn, context) {
  let result

  return function () {
    if (fn) {
      result = fn.apply(context || this, arguments)
      fn = null
    }

    return result
  }
}

export function once(fn, context) {
  if (arguments.length === 1) {
    const wrap = onceFn(fn, context)

    return curry(wrap)
  }

  return onceFn(fn, context)
}

Tests

import {once} from './once'

test('with counter', () => {
  let counter = 0
  const runOnce = once(x => {
    counter++

    return x + 2
  })
  expect(runOnce(1)).toEqual(3)
  runOnce(1)
  runOnce(1)
  runOnce(1)
  expect(counter).toEqual(1)
})

test('happy path', () => {
  const addOneOnce = once((a, b, c) => a + b + c, 1)

  expect(addOneOnce(10, 20, 30)).toBe(60)
  expect(addOneOnce(40)).toEqual(60)
})

Typescript test

import {once} from 'rambda'

describe('R.once', () => {
  it('happy', () => {
    const runOnce = once((x: number) => {
      return x + 2
    })

    const result = runOnce(1)
    result // $ExpectType number
  })
})

or

Logical OR

R.or(false, true); // => true
R.or(false, false); // => false
R.or(false, 'foo'); // => 'foo'

Try this R.or example in Rambda REPL

over

over<T>(lens: Lens, fn: Arity1Fn, value: T): T

It returns a copied Object or Array with modified value received by applying function fn to lens focus.

const headLens = R.lensIndex(0)
 
R.over(headLens, R.toUpper, ['foo', 'bar', 'baz']) // => ['FOO', 'bar', 'baz']

Try this R.over example in Rambda REPL

All Typescript definitions

over<T>(lens: Lens, fn: Arity1Fn, value: T): T;
over<T>(lens: Lens, fn: Arity1Fn, value: T[]): T[];
over(lens: Lens, fn: Arity1Fn): <T>(value: T) => T;
over(lens: Lens, fn: Arity1Fn): <T>(value: T[]) => T[];
over(lens: Lens): <T>(fn: Arity1Fn, value: T) => T;
over(lens: Lens): <T>(fn: Arity1Fn, value: T[]) => T[];

R.over source

import {curry} from './curry'

const Identity = x => ({
  x,
  map: fn => Identity(fn(x)),
})

function overFn(lens, fn, object) {
  return lens(x => Identity(fn(x)))(object).x
}

export const over = curry(overFn)

Tests

import {assoc} from './assoc'
import {lens} from './lens'
import {lensIndex} from './lensIndex'
import {lensPath} from './lensPath'
import {over} from './over'
import {prop} from './prop'
import {toUpper} from './toUpper'

const testObject = {
  foo: 'bar',
  baz: {
    a: 'x',
    b: 'y',
  },
}

test('assoc lens', () => {
  const assocLens = lens(prop('foo'), assoc('foo'))
  const result = over(assocLens, toUpper, testObject)
  const expected = {
    ...testObject,
    foo: 'BAR',
  }
  expect(result).toEqual(expected)
})

test('path lens', () => {
  const pathLens = lensPath('baz.a')
  const result = over(pathLens, toUpper, testObject)
  const expected = {
    ...testObject,
    baz: {
      a: 'X',
      b: 'y',
    },
  }
  expect(result).toEqual(expected)
})

test('index lens', () => {
  const indexLens = lensIndex(0)
  const result = over(indexLens, toUpper)(['foo', 'bar'])
  expect(result).toEqual(['FOO', 'bar'])
})

Rambda is faster than Ramda with 56.23%

const R = require('../../dist/rambda.js')

const testObj = {a: 1}

const last = [
  {
    label: 'Rambda',
    fn: () => {
      R.over(R.lensProp('a'), R.inc, testObj)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.over(Ramda.lensProp('a'), Ramda.inc, testObj)
    },
  },
]

partial

partial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T

It is very similar to R.curry, but you can pass initial arguments when you create the curried function.

R.partial will keep returning a function until all the arguments that the function fn expects are passed. The name comes from the fact that you partially inject the inputs.

💥 Rambda's partial doesn't need the input arguments to be wrapped as array.

const fn = (title, firstName, lastName) => {
  return title + ' ' + firstName + ' ' + lastName + '!'
}

const canPassAnyNumberOfArguments = R.partial(fn, 'Hello')
const ramdaStyle = R.partial(fn, ['Hello'])

const finalFn = canPassAnyNumberOfArguments('Foo')

finalFn('Bar') // =>  'Hello, Foo Bar!'

Try this R.partial example in Rambda REPL

All Typescript definitions

partial<V0, V1, T>(fn: (x0: V0, x1: V1) => T, args: [V0]): (x1: V1) => T;
partial<V0, V1, V2, T>(fn: (x0: V0, x1: V1, x2: V2) => T, args: [V0, V1]): (x2: V2) => T;
partial<V0, V1, V2, T>(fn: (x0: V0, x1: V1, x2: V2) => T, args: [V0]): (x1: V1, x2: V2) => T;
partial<V0, V1, V2, V3, T>(fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, args: [V0, V1, V2]): (x2: V3) => T;
partial<V0, V1, V2, V3, T>(fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, args: [V0, V1]): (x2: V2, x3: V3) => T;
partial<V0, V1, V2, V3, T>(fn: (x0: V0, x1: V1, x2: V2, x3: V3) => T, args: [V0]): (x1: V1, x2: V2, x3: V3) => T;
partial<T>(fn: (...a: any[]) => T, args: any[]): (...x: any[]) => T;

R.partial source

export function partial(fn, ...args) {
  const len = fn.length

  return (...rest) => {
    if (args.length + rest.length >= len) {
      return fn(...args, ...rest)
    }

    return partial(fn, ...[...args, ...rest])
  }
}

Tests

import {partial} from './partial'
import {type} from './type'

const greet = (salutation, title, firstName, lastName) =>
  salutation + ', ' + title + ' ' + firstName + ' ' + lastName + '!'

test('happy', () => {
  const canPassAnyNumberOfArguments = partial(greet, 'Hello', 'Ms.')
  const fn = canPassAnyNumberOfArguments('foo')
  const sayHello = partial(greet, ['Hello'])
  const sayHelloRamda = partial(sayHello, ['Ms.'])

  expect(type(fn)).toBe('Function')

  expect(fn('bar')).toBe('Hello, Ms. foo bar!')
  expect(sayHelloRamda('foo', 'bar')).toBe('Hello, Ms. foo bar!')
})

test('extra arguments are ignored', () => {
  const canPassAnyNumberOfArguments = partial(greet, 'Hello', 'Ms.')
  const fn = canPassAnyNumberOfArguments('foo')

  expect(type(fn)).toBe('Function')

  expect(fn('bar', 1, 2)).toBe('Hello, Ms. foo bar!')
})

test('when array is input', () => {
  const fooFn = (a, b, c, d) => ({
    a,
    b,
    c,
    d,
  })
  const barFn = partial(fooFn, [1, 2], [])

  expect(barFn(1, 2)).toEqual({
    a: [1, 2],
    b: [],
    c: 1,
    d: 2,
  })
})

test('ramda spec', () => {
  const sayHello = partial(greet, 'Hello')
  const sayHelloToMs = partial(sayHello, 'Ms.')

  expect(sayHelloToMs('Jane', 'Jones')).toBe('Hello, Ms. Jane Jones!')
})

Typescript test

import {partial} from 'rambda'

describe('R.partial', () => {
  it('happy', () => {
    function greet(
      salutation: string,
      title: string,
      firstName: string,
      lastName: string
    ) {
      return `${salutation}, ${title} ${firstName} ${lastName}!`
    }

    const sayHello = partial(greet, ['Hello'])
    const sayHelloToMs = partial(sayHello, ['Ms.'])
    const result = sayHelloToMs('Jane', 'Jones')
    result // $ExpectType string
  })
})

partition

partition<T>(
  predicate: Predicate<T>,
  input: T[]
): [T[], T[]]

It will return array of two objects/arrays according to predicate function. The first member holds all instances of input that pass the predicate function, while the second member - those who doesn't.

const list = [1, 2, 3]
const obj = {a: 1, b: 2, c: 3}
const predicate = x => x > 2

const result = [
  R.partition(predicate, list),
  R.partition(predicate, obj)
]
const expected = [
  [[3], [1, 2]],
  [{c: 3},  {a: 1, b: 2}],
]
// `result` is equal to `expected`

Try this R.partition example in Rambda REPL

All Typescript definitions

partition<T>(
  predicate: Predicate<T>,
  input: T[]
): [T[], T[]];
partition<T>(
  predicate: Predicate<T>
): (input: T[]) => [T[], T[]];
partition<T>(
  predicate: (x: T, prop?: string) => boolean,
  input: { [key: string]: T}
): [{ [key: string]: T}, { [key: string]: T}];
partition<T>(
  predicate: (x: T, prop?: string) => boolean
): (input: { [key: string]: T}) => [{ [key: string]: T}, { [key: string]: T}];

R.partition source

import {_isArray} from './_internals/_isArray'

export function partitionObject(predicate, iterable) {
  const yes = {}
  const no = {}
  Object.entries(iterable).forEach(([prop, value]) => {
    if (predicate(value, prop)) {
      yes[prop] = value
    } else {
      no[prop] = value
    }
  })

  return [yes, no]
}

export function partitionArray(predicate, list, indexed = false) {
  const yes = []
  const no = []
  let counter = -1

  while (counter++ < list.length - 1) {
    if (
      indexed ? predicate(list[counter], counter) : predicate(list[counter])
    ) {
      yes.push(list[counter])
    } else {
      no.push(list[counter])
    }
  }

  return [yes, no]
}

export function partition(predicate, iterable) {
  if (arguments.length === 1) {
    return listHolder => partition(predicate, listHolder)
  }
  if (!_isArray(iterable)) return partitionObject(predicate, iterable)

  return partitionArray(predicate, iterable)
}

Tests

import {partition} from './partition'

test('with array', () => {
  const predicate = x => x > 2
  const list = [1, 2, 3, 4]

  const result = partition(predicate, list)
  const expectedResult = [
    [3, 4],
    [1, 2],
  ]

  expect(result).toEqual(expectedResult)
})

test('with object', () => {
  const predicate = (value, prop) => {
    expect(typeof prop).toBe('string')

    return value > 2
  }
  const hash = {
    a: 1,
    b: 2,
    c: 3,
    d: 4,
  }

  const result = partition(predicate)(hash)
  const expectedResult = [
    {
      c: 3,
      d: 4,
    },
    {
      a: 1,
      b: 2,
    },
  ]

  expect(result).toEqual(expectedResult)
})

test('readme example', () => {
  const list = [1, 2, 3]
  const obj = {
    a: 1,
    b: 2,
    c: 3,
  }
  const predicate = x => x > 2

  const result = [partition(predicate, list), partition(predicate, obj)]
  const expected = [
    [[3], [1, 2]],
    [
      {c: 3},
      {
        a: 1,
        b: 2,
      },
    ],
  ]
  expect(result).toEqual(expected)
})

Typescript test

import {partition} from 'rambda'

describe('R.partition', () => {
  it('with array', () => {
    const predicate = (x: number) => {
      return x > 2
    }
    const list = [1, 2, 3, 4]

    const result = partition(predicate, list)
    const curriedResult = partition(predicate)(list)
    result // $ExpectType [number[], number[]]
    curriedResult // $ExpectType [number[], number[]]
  })

  /*
    TODO
    revert to old version of `dtslint` and `R.partition` typing
    as there is diff between VSCode types(correct) and dtslint(incorrect)
    
    it('with object', () => {
      const predicate = (value: number, prop?: string) => {
        return value > 2
      }
      const hash = {
        a: 1,
        b: 2,
        c: 3,
        d: 4,
      }
  
      const result = partition(predicate, hash)
      const curriedResult = partition(predicate)(hash)
      result[0] // $xExpectType { [key: string]: number; }
      result[1] // $xExpectType { [key: string]: number; }
      curriedResult[0] // $xExpectType { [key: string]: number; }
      curriedResult[1] // $xExpectType { [key: string]: number; }
    })
    */
})

path

path<Input, T>(pathToSearch: Path, obj: Input): T | undefined

If pathToSearch is 'a.b' then it will return 1 if obj is {a:{b:1}}.

It will return undefined, if such path is not found.

💥 String anotation of pathToSearch is one of the differences between Rambda and Ramda.

const obj = {a: {b: 1}}
const pathToSearch = 'a.b'
const pathToSearchList = ['a', 'b']

const result = [
  R.path(pathToSearch, obj),
  R.path(pathToSearchList, obj),
  R.path('a.b.c.d', obj)
]
// => [1, 1, undefined]

Try this R.path example in Rambda REPL

All Typescript definitions

path<Input, T>(pathToSearch: Path, obj: Input): T | undefined;
path<T>(pathToSearch: Path, obj: any): T | undefined;
path<T>(pathToSearch: Path): (obj: any) => T | undefined;
path<Input, T>(pathToSearch: Path): (obj: Input) => T | undefined;

R.path source

export function path(pathInput, obj) {
  if (arguments.length === 1) return _obj => path(pathInput, _obj)

  if (obj === null || obj === undefined) {
    return undefined
  }
  let willReturn = obj
  let counter = 0

  const pathArrValue =
    typeof pathInput === 'string' ? pathInput.split('.') : pathInput

  while (counter < pathArrValue.length) {
    if (willReturn === null || willReturn === undefined) {
      return undefined
    }
    if (willReturn[pathArrValue[counter]] === null) return undefined

    willReturn = willReturn[pathArrValue[counter]]
    counter++
  }

  return willReturn
}

Tests

import {path} from './path'

test('with array inside object', () => {
  const obj = {a: {b: [1, {c: 1}]}}

  expect(path('a.b.1.c', obj)).toBe(1)
})

test('works with undefined', () => {
  const obj = {a: {b: {c: 1}}}

  expect(path('a.b.c.d.f', obj)).toBeUndefined()
  expect(path('foo.babaz', undefined)).toBeUndefined()
  expect(path('foo.babaz')(undefined)).toBeUndefined()
})

test('works with string instead of array', () => {
  expect(path('foo.bar.baz')({foo: {bar: {baz: 'yes'}}})).toEqual('yes')
})

test('path', () => {
  expect(path(['foo', 'bar', 'baz'])({foo: {bar: {baz: 'yes'}}})).toEqual(
    'yes'
  )

  expect(path(['foo', 'bar', 'baz'])(null)).toBeUndefined()

  expect(path(['foo', 'bar', 'baz'])({foo: {bar: 'baz'}})).toBeUndefined()
})

test('null is not a valid path', () => {
  expect(path('audio_tracks', {a: 1, audio_tracks: null})).toBeUndefined()
})

Typescript test

import {path} from 'rambda'

interface Input {
  a: number
  b: {
    c: boolean
  }
}

describe('R.path', () => {
  it('without specified input type', () => {
    const input = {a: 1, b: {c: true}}
    const result = path<boolean>('a.b.c', input)
    const curriedResult = path<boolean>('a.b.c')(input)
    result // $ExpectType boolean | undefined
    curriedResult // $ExpectType boolean | undefined
  })

  it('without specified output type', () => {
    const input = {a: 1, b: {c: true}}
    const result = path('a.b.c', input)
    result // $ExpectType unknown
  })

  it('with string as path', () => {
    const input: Input = {a: 1, b: {c: true}}
    const resultA = path<boolean>('a.b.c', input)
    const resultB = path<boolean>('a.b.c')(input)
    resultA // $ExpectType boolean | undefined
    resultB // $ExpectType boolean | undefined
  })
  it('with array as path', () => {
    const input: Input = {a: 1, b: {c: true}}
    const resultA = path<boolean>(['a', 'b', 'c'], input)
    const resultB = path<boolean>(['a', 'b', 'c'])(input)
    resultA // $ExpectType boolean | undefined
    resultB // $ExpectType boolean | undefined
  })
})

describe('path with specified input', () => {
  it('with string as path', () => {
    const input: Input = {a: 1, b: {c: true}}
    // const wrongInput = { a: 1, b: true }
    // const resultA = path<Input, boolean>('a.b.c', wrongInput)
    const resultA = path<Input, boolean>('a.b.c', input)
    const resultB = path<Input, boolean>('a.b.c')(input)
    resultA // $ExpectType boolean | undefined
    resultB // $ExpectType boolean | undefined
  })
  it('with array as path', () => {
    const input: Input = {a: 1, b: {c: true}}
    const resultA = path<Input, boolean>(['a', 'b', 'c'], input)
    const resultB = path<Input, boolean>(['a', 'b', 'c'])(input)
    resultA // $ExpectType boolean | undefined
    resultB // $ExpectType boolean | undefined
  })
})

Lodash is fastest. Rambda is 37.81% slower and Ramda is 77.81% slower

const R = require('../../dist/rambda.js')

const obj = {a: {b: 2}}
const pathInput = ['a', 'b']

const path = [
  {
    label: 'Rambda',
    fn: () => {
      R.path(pathInput, obj)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.path(pathInput, obj)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.get(obj, pathInput)
    },
  },
]

pathEq

pathEq(pathToSearch: Path, target: any, input: any): boolean

It returns true if pathToSearch of input object is equal to target value.

pathToSearch is passed to R.path, which means that it can be either a string or an array. Also equality between target and the found value is determined by R.equals.

const path = 'a.b'
const target = {c: 1}
const input = {a: {b: {c: 1}}}

const result = R.pathEq(
  path,
  target,
  input
)
// => true

Try this R.pathEq example in Rambda REPL

All Typescript definitions

pathEq(pathToSearch: Path, target: any, input: any): boolean;
pathEq(pathToSearch: Path, target: any): (input: any) => boolean;
pathEq(pathToSearch: Path): (target: any) => (input: any) => boolean;

R.pathEq source

import {curry} from './curry'
import {equals} from './equals'
import {path} from './path'

function pathEqFn(pathToSearch, target, input) {
  return equals(path(pathToSearch, input), target)
}

export const pathEq = curry(pathEqFn)

Tests

import {pathEq} from './pathEq'

test('when true', () => {
  const path = 'a.b'
  const obj = {a: {b: {c: 1}}}
  const target = {c: 1}

  expect(pathEq(path, target, obj)).toBeTrue()
})

test('when false', () => {
  const path = 'a.b'
  const obj = {a: {b: 1}}
  const target = 2

  expect(pathEq(path, target)(obj)).toBeFalse()
})

test('when wrong path', () => {
  const path = 'foo.bar'
  const obj = {a: {b: 1}}
  const target = 2

  expect(pathEq(path, target, obj)).toBeFalse()
})

Typescript test

import {pathEq} from 'rambda'

describe('R.pathEq', () => {
  it('with string path', () => {
    const pathToSearch = 'a.b.c'
    const input = {a: {b: {c: 1}}}
    const target = {c: 1}

    const result = pathEq(pathToSearch, input, target)
    const curriedResult = pathEq(pathToSearch, input, target)
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })

  it('with array path', () => {
    const pathToSearch = ['a', 'b', 'c']
    const input = {a: {b: {c: 1}}}
    const target = {c: 1}

    const result = pathEq(pathToSearch, input, target)
    const curriedResult = pathEq(pathToSearch, input, target)
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

describe('with ramda specs', () => {
  const testPath = ['x', 0, 'y']
  const testObj = {
    x: [
      {y: 2, z: 3},
      {y: 4, z: 5},
    ],
  }

  const result1 = pathEq(testPath, 2, testObj)
  const result2 = pathEq(testPath, 2)(testObj)
  const result3 = pathEq(testPath)(2)(testObj)
  result1 // $ExpectType boolean
  result2 // $ExpectType boolean
  result3 // $ExpectType boolean
})

pathOr

pathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T

It reads obj input and returns either R.path(pathToSearch, obj) result or defaultValue input.

const defaultValue = 'DEFAULT_VALUE'
const pathToSearch = 'a.b'
const pathToSearchList = ['a', 'b']

const obj = {
  a : {
    b : 1
  }
}

const result = [
  R.pathOr(DEFAULT_VALUE, pathToSearch, obj),
  R.pathOr(DEFAULT_VALUE, pathToSearchList, obj), 
  R.pathOr(DEFAULT_VALUE, 'a.b.c', obj)
]
// => [1, 1, 'DEFAULT_VALUE']

Try this R.pathOr example in Rambda REPL

All Typescript definitions

pathOr<T>(defaultValue: T, pathToSearch: Path, obj: any): T;
pathOr<T>(defaultValue: T, pathToSearch: Path): (obj: any) => T;
pathOr<T>(defaultValue: T): (pathToSearch: Path) => (obj: any) => T;

R.pathOr source

import {curry} from './curry'
import {defaultTo} from './defaultTo'
import {path} from './path'

function pathOrFn(defaultValue, pathInput, obj) {
  return defaultTo(defaultValue, path(pathInput, obj))
}

export const pathOr = curry(pathOrFn)

Tests

import {pathOr} from './pathOr'

test('with undefined', () => {
  const result = pathOr('foo', 'x.y', {x: {y: 1}})

  expect(result).toEqual(1)
})

test('with null', () => {
  const result = pathOr('foo', 'x.y', null)

  expect(result).toEqual('foo')
})

test('with NaN', () => {
  const result = pathOr('foo', 'x.y', NaN)

  expect(result).toEqual('foo')
})

test('curry case (x)(y)(z)', () => {
  const result = pathOr('foo')('x.y.z')({x: {y: {a: 1}}})

  expect(result).toEqual('foo')
})

test('curry case (x)(y,z)', () => {
  const result = pathOr('foo', 'x.y.z')({x: {y: {a: 1}}})

  expect(result).toEqual('foo')
})

test('curry case (x,y)(z)', () => {
  const result = pathOr('foo')('x.y.z', {x: {y: {a: 1}}})

  expect(result).toEqual('foo')
})

Typescript test

import {pathOr} from 'rambda'

describe('R.pathOr', () => {
  it('with string path', () => {
    const x = pathOr<string>('foo', 'x.y', {x: {y: 'bar'}})
    x // $ExpectType string
  })
  it('with array path', () => {
    const x = pathOr<string>('foo', ['x', 'y'], {x: {y: 'bar'}})
    x // $ExpectType string
  })
  it('without passing type looks bad', () => {
    const x = pathOr('foo', 'x.y', {x: {y: 'bar'}})
    x // $ExpectType "foo"
  })
  it('curried', () => {
    const x = pathOr<string>('foo', 'x.y')({x: {y: 'bar'}})
    x // $ExpectType string
  })
})

paths

paths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[]

It loops over members of pathsToSearch as singlePath and returns the array produced by R.path(singlePath, obj).

Because it calls R.path, then singlePath can be either string or a list.

const obj = {
  a : {
    b : {
      c : 1,
      d : 2
    }
  }
}

const result = R.paths([
  'a.b.c',
  'a.b.d',
  'a.b.c.d.e',
], obj)
// => [1, 2, undefined]

Try this R.paths example in Rambda REPL

All Typescript definitions

paths<Input, T>(pathsToSearch: Path[], obj: Input): (T | undefined)[];
paths<Input, T>(pathsToSearch: Path[]): (obj: Input) => (T | undefined)[];
paths<T>(pathsToSearch: Path[], obj: any): (T | undefined)[];
paths<T>(pathsToSearch: Path[]): (obj: any) => (T | undefined)[];

R.paths source

import {path} from './path'

export function paths(pathsToSearch, obj) {
  if (arguments.length === 1) {
    return _obj => paths(pathsToSearch, _obj)
  }

  return pathsToSearch.map(singlePath => path(singlePath, obj))
}

Tests

import {paths} from './paths'

const obj = {
  a: {
    b: {
      c: 1,
      d: 2,
    },
  },
  p: [{q: 3}],
  x: {
    y: 'FOO',
    z: [[{}]],
  },
}

test('with string path + curry', () => {
  const pathsInput = ['a.b.d', 'p.q']
  const expected = [2, undefined]
  const result = paths(pathsInput, obj)
  const curriedResult = paths(pathsInput)(obj)

  expect(result).toEqual(expected)
  expect(curriedResult).toEqual(expected)
})

test('with array path', () => {
  const result = paths(
    [
      ['a', 'b', 'c'],
      ['x', 'y'],
    ],
    obj
  )

  expect(result).toEqual([1, 'FOO'])
})

test('takes a paths that contains indices into arrays', () => {
  expect(
    paths(
      [
        ['p', 0, 'q'],
        ['x', 'z', 0, 0],
      ],
      obj
    )
  ).toEqual([3, {}])
  expect(
    paths(
      [
        ['p', 0, 'q'],
        ['x', 'z', 2, 1],
      ],
      obj
    )
  ).toEqual([3, undefined])
})

test("gets a deep property's value from objects", () => {
  expect(paths([['a', 'b']], obj)).toEqual([obj.a.b])
  expect(paths([['p', 0]], obj)).toEqual([obj.p[0]])
})

test('returns undefined for items not found', () => {
  expect(paths([['a', 'x', 'y']], obj)).toEqual([undefined])
  expect(paths([['p', 2]], obj)).toEqual([undefined])
})

Typescript test

import {paths} from 'rambda'

interface Input {
  a: number
  b: number
  c: number
}

const input: Input = {a: 1, b: 2, c: 3}

describe('R.paths', () => {
  it('with dot notation', () => {
    const result = paths<number>(['a.b.c', 'foo.bar'], input)
    result // $ExpectType (number | undefined)[]
  })

  it('without type', () => {
    const result = paths(['a.b.c', 'foo.bar'], input)
    result // $ExpectType unknown[]
  })

  it('with array as path', () => {
    const result = paths<number>([['a', 'b', 'c'], ['foo.bar']], input)
    result // $ExpectType (number | undefined)[]
  })

  it('curried', () => {
    const result = paths<number>([['a', 'b', 'c'], ['foo.bar']])(input)
    result // $ExpectType (number | undefined)[]
  })
})

pick

pick<T, K extends string | number | symbol>(propsToPick: K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>

It returns a partial copy of an input containing only propsToPick properties.

input can be either an object or an array.

String anotation of propsToPick is one of the differences between Rambda and Ramda.

💥 When using this method with TypeScript, it is much easier to pass propsToPick as an array. If passing a string, you will need to explicitly declare the output type.

const obj = {
  a : 1,
  b : false,
  foo: 'cherry'
}
const list = [1, 2, 3, 4]
const propsToPick = 'a,foo'
const propsToPickList = ['a', 'foo']

const result = [
  R.pick(propsToPick, obj),
  R.pick(propsToPickList, obj),
  R.pick('a,bar', obj),
  R.pick('bar', obj),
  R.pick([0, 3, 5], list),
  R.pick('0,3,5', list),
]

const expected = [
  {a:1, foo: 'cherry'},
  {a:1, foo: 'cherry'},
  {a:1},
  {},
  {0: 1, 3: 4},
  {0: 1, 3: 4},
]
// => `result` is equal to `expected`

Try this R.pick example in Rambda REPL

All Typescript definitions

pick<T, K extends string | number | symbol>(propsToPick: K[], input: T): Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>;
pick<K extends string | number | symbol>(propsToPick: K[]): <T>(input: T) => Pick<T, Exclude<keyof T, Exclude<keyof T, K>>>;
pick<T, U>(propsToPick: string, input: T): U;
pick<T, U>(propsToPick: string): (input: T) => U;
pick<T>(propsToPick: string, input: object): T;
pick<T>(propsToPick: string): (input: object) => T;

R.pick source

export function pick(propsToPick, input) {
  if (arguments.length === 1) return _input => pick(propsToPick, _input)

  if (input === null || input === undefined) {
    return undefined
  }
  const keys =
    typeof propsToPick === 'string' ? propsToPick.split(',') : propsToPick

  const willReturn = {}
  let counter = 0

  while (counter < keys.length) {
    if (keys[counter] in input) {
      willReturn[keys[counter]] = input[keys[counter]]
    }
    counter++
  }

  return willReturn
}

Tests

import {pick} from './pick'

const obj = {
  a: 1,
  b: 2,
  c: 3,
}

test('props to pick is a string', () => {
  const result = pick('a,c', obj)
  const resultCurry = pick('a,c')(obj)
  const expectedResult = {
    a: 1,
    c: 3,
  }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('when prop is missing', () => {
  const result = pick('a,d,f', obj)
  expect(result).toEqual({a: 1})
})

test('with list indexes as props', () => {
  const list = [1, 2, 3]
  const expected = {0: 1, 2: 3}
  expect(pick([0, 2, 3], list)).toEqual(expected)
  expect(pick('0,2,3', list)).toEqual(expected)
})

test('props to pick is an array', () => {
  expect(
    pick(['a', 'c'])({
      a: 'foo',
      b: 'bar',
      c: 'baz',
    })
  ).toEqual({
    a: 'foo',
    c: 'baz',
  })

  expect(
    pick(['a', 'd', 'e', 'f'])({
      a: 'foo',
      b: 'bar',
      c: 'baz',
    })
  ).toEqual({a: 'foo'})

  expect(pick('a,d,e,f')(null)).toEqual(undefined)
})

test('works with list as input and number as props - props to pick is an array', () => {
  const result = pick([1, 2], ['a', 'b', 'c', 'd'])
  expect(result).toEqual({
    1: 'b',
    2: 'c',
  })
})

test('works with list as input and number as props - props to pick is a string', () => {
  const result = pick('1,2', ['a', 'b', 'c', 'd'])
  expect(result).toEqual({
    1: 'b',
    2: 'c',
  })
})

test('with symbol', () => {
  const symbolProp = Symbol('s')
  expect(pick([symbolProp], {[symbolProp]: 'a'})).toMatchInlineSnapshot(`
    Object {
      Symbol(s): "a",
    }
  `)
})

Typescript test

import {pick} from 'rambda'

const input = {a: 'foo', b: 2, c: 3, d: 4}

describe('R.pick with array as props input', () => {
  it('without passing type', () => {
    const result = pick(['a', 'c'], input)
    result.a // $ExpectType string
    result.c // $ExpectType number
  })
})

describe('R.pick with string as props input', () => {
  interface Input {
    a: string
    b: number
    c: number
    d: number
  }
  interface Output {
    a: string
    c: number
  }
  it('explicitly declare output', () => {
    const result = pick<Output>('a,c', input)
    result // $ExpectType Output
    result.a // $ExpectType string
    result.c // $ExpectType number

    const curriedResult = pick<Output>('a,c')(input)

    curriedResult.a // $ExpectType string
  })

  it('explicitly declare input and output', () => {
    const result = pick<Input, Output>('a,c', input)
    result // $ExpectType Output
    result.a // $ExpectType string

    const curriedResult = pick<Input, Output>('a,c')(input)

    curriedResult.a // $ExpectType string
  })

  it('without passing type', () => {
    const result = pick('a,c', input)
    result // $ExpectType unknown
  })
})

Rambda is fastest. Ramda is 19.07% slower and Lodash is 80.2% slower

const R = require('../../dist/rambda.js')

const obj = {
  a: 'foo',
  b: 'bar',
  c: 'baz',
}
const pickInput = ['a', 'c']
const pick = [
  {
    label: 'Rambda',
    fn: () => {
      R.pick(pickInput, obj)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.pick(pickInput, obj)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.pick(obj, pickInput)
    },
  },
]

pickAll

pickAll<T, U>(propsToPick: string[], input: T): U

Same as R.pick but it won't skip the missing props, i.e. it will assign them to undefined.

💥 When using this method with TypeScript, it is much easier to pass propsToPick as an array. If passing a string, you will need to explicitly declare the output type.

const obj = {
  a : 1,
  b : false,
  foo: 'cherry'
}
const propsToPick = 'a,foo,bar'
const propsToPickList = ['a', 'foo', 'bar']

const result = [
  R.pickAll(propsToPick, obj),
  R.pickAll(propsToPickList, obj),
  R.pickAll('a,bar', obj),
  R.pickAll('bar', obj),
]
const expected = [
  {a:1, foo: 'cherry', bar: undefined},
  {a:1, foo: 'cherry', bar: undefined},
  {a:1, bar: undefined},
  {bar: undefined}
]
// => `result` is equal to `expected`

Try this R.pickAll example in Rambda REPL

All Typescript definitions

pickAll<T, U>(propsToPick: string[], input: T): U;
pickAll<T, U>(propsToPick: string[]): (input: T) => U;
pickAll<T, U>(propsToPick: string, input: T): U;
pickAll<T, U>(propsToPick: string): (input: T) => U;

R.pickAll source

export function pickAll(propsToPick, obj) {
  if (arguments.length === 1) return _obj => pickAll(propsToPick, _obj)

  if (obj === null || obj === undefined) {
    return undefined
  }
  const keysValue =
    typeof propsToPick === 'string' ? propsToPick.split(',') : propsToPick

  const willReturn = {}
  let counter = 0

  while (counter < keysValue.length) {
    if (keysValue[counter] in obj) {
      willReturn[keysValue[counter]] = obj[keysValue[counter]]
    } else {
      willReturn[keysValue[counter]] = undefined
    }
    counter++
  }

  return willReturn
}

Tests

import {pickAll} from './pickAll'

test('when input is undefined or null', () => {
  expect(pickAll('a', null)).toBe(undefined)
  expect(pickAll('a', undefined)).toBe(undefined)
})

test('with string as condition', () => {
  const obj = {
    a: 1,
    b: 2,
    c: 3,
  }
  const result = pickAll('a,c', obj)
  const resultCurry = pickAll('a,c')(obj)
  const expectedResult = {
    a: 1,
    b: undefined,
    c: 3,
  }

  expect(result).toEqual(expectedResult)
  expect(resultCurry).toEqual(expectedResult)
})

test('with array as condition', () => {
  expect(
    pickAll(['a', 'b', 'c'], {
      a: 'foo',
      c: 'baz',
    })
  ).toEqual({
    a: 'foo',
    b: undefined,
    c: 'baz',
  })
})

Typescript test

import {pickAll} from 'rambda'

interface Input {
  a: string
  b: number
  c: number
  d: number
}
interface Output {
  a?: string
  c?: number
}
const input = {a: 'foo', b: 2, c: 3, d: 4}

describe('R.pickAll with array as props input', () => {
  it('without passing type', () => {
    const result = pickAll(['a', 'c'], input)
    result // $ExpectType unknown
  })
  it('without passing type + curry', () => {
    const result = pickAll(['a', 'c'])(input)
    result // $ExpectType unknown
  })
  it('explicitly passing types', () => {
    const result = pickAll<Input, Output>(['a', 'c'], input)
    result.a // $ExpectType string | undefined
    result.c // $ExpectType number | undefined
  })
  it('explicitly passing types + curry', () => {
    const result = pickAll<Input, Output>(['a', 'c'])(input)
    result.a // $ExpectType string | undefined
    result.c // $ExpectType number | undefined
  })
})

describe('R.pickAll with string as props input', () => {
  it('without passing type', () => {
    const result = pickAll('a,c', input)
    result // $ExpectType unknown
  })
  it('without passing type + curry', () => {
    const result = pickAll('a,c')(input)
    result // $ExpectType unknown
  })
  it('explicitly passing types', () => {
    const result = pickAll<Input, Output>('a,c', input)
    result.a // $ExpectType string | undefined
    result.c // $ExpectType number | undefined
  })
  it('explicitly passing types + curry', () => {
    const result = pickAll<Input, Output>('a,c')(input)
    result.a // $ExpectType string | undefined
    result.c // $ExpectType number | undefined
  })
})

pipe

It performs left-to-right function composition.

const result = R.pipe(
  R.filter(val => val > 2),
  R.map(a => a * 2)
)([1, 2, 3, 4])

// => [6, 8]

Try this R.pipe example in Rambda REPL

pluck

pluck<K extends keyof T, T>(property: K, list: T[]): T[K][]

It returns list of the values of property taken from the all objects inside list.

const list = [{a: 1}, {a: 2}, {b: 3}]
const property = 'a'

const result = R.pluck(property, list) 
// => [1, 2]

Try this R.pluck example in Rambda REPL

All Typescript definitions

pluck<K extends keyof T, T>(property: K, list: T[]): T[K][];
pluck<T>(property: number, list: { [k: number]: T }[]):  T[];
pluck<P extends string>(property: P): <T>(list: Record<P, T>[]) => T[];
pluck(property: number): <T>(list: { [k: number]: T }[]) => T[];

R.pluck source

import {map} from './map'

export function pluck(property, list) {
  if (arguments.length === 1) return _list => pluck(property, _list)

  const willReturn = []

  map(x => {
    if (x[property] !== undefined) {
      willReturn.push(x[property])
    }
  }, list)

  return willReturn
}

Tests

import {pluck} from './pluck'

test('happy', () => {
  expect(pluck('a')([{a: 1}, {a: 2}, {b: 1}])).toEqual([1, 2])
})

test('with number', () => {
  const input = [
    [1, 2],
    [3, 4],
  ]

  expect(pluck(0, input)).toEqual([1, 3])
})

Typescript test

import {pluck} from 'rambda'

describe('R.pluck', () => {
  it('with object', () => {
    interface ListMember {
      a: number
      b: string
    }
    const input: ListMember[] = [
      {a: 1, b: 'foo'},
      {a: 2, b: 'bar'},
    ]
    const resultA = pluck('a', input)
    const resultB = pluck('b')(input)
    resultA // $ExpectType number[]
    resultB // $ExpectType string[]
  })

  it('with array', () => {
    const input = [
      [1, 2],
      [3, 4],
      [5, 6],
    ]
    const result = pluck(0, input)
    const resultCurry = pluck(0)(input)
    result // $ExpectType number[]
    resultCurry // $ExpectType number[]
  })
})

prepend

prepend<T>(x: T, input: T[]): T[]

It adds element x at the beginning of list.

const result = R.prepend('foo', ['bar', 'baz'])
// => ['foo', 'bar', 'baz']

Try this R.prepend example in Rambda REPL

All Typescript definitions

prepend<T>(x: T, input: T[]): T[];
prepend<T>(x: T): (input: T[]) => T[];

R.prepend source

export function prepend(x, input) {
  if (arguments.length === 1) return _input => prepend(x, _input)

  if (typeof input === 'string') return [x].concat(input.split(''))

  return [x].concat(input)
}

Tests

import {prepend} from './prepend'

test('happy', () => {
  expect(prepend('yes', ['foo', 'bar', 'baz'])).toEqual([
    'yes',
    'foo',
    'bar',
    'baz',
  ])
})

test('with empty list', () => {
  expect(prepend('foo')([])).toEqual(['foo'])
})

test('with string instead of array', () => {
  expect(prepend('foo')('bar')).toEqual(['foo', 'b', 'a', 'r'])
})

Typescript test

import {prepend} from 'rambda'

const list = [1, 2, 3]

describe('R.prepend', () => {
  it('happy', () => {
    const result = prepend(4, list)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = prepend(4)(list)

    result // $ExpectType number[]
  })
})

product

product(list: number[]): number

R.product([ 2, 3, 4 ])
// => 24)

Try this R.product example in Rambda REPL

All Typescript definitions

product(list: number[]): number;

R.product source

import {multiply} from './multiply'
import {reduce} from './reduce'

export const product = reduce(multiply, 1)

Tests

import {product} from './product'

test('happy', () => {
  expect(product([2, 3, 4])).toEqual(24)
})

test('bad input', () => {
  expect(product([null])).toEqual(0)
  expect(product([])).toEqual(1)
})

Typescript test

import {product} from 'rambda'

describe('R.product', () => {
  it('happy', () => {
    const result = product([1, 2, 3])

    result // $ExpectType number
  })
})

prop

prop<P extends keyof O, O>(propToFind: P, obj: O): O[P]

It returns the value of property propToFind in obj.

If there is no such property, it returns undefined.

const result = [
  R.prop('x', {x: 100}), 
  R.prop('x', {a: 1}) 
]
// => [100, undefined]

Try this R.prop example in Rambda REPL

All Typescript definitions

prop<P extends keyof O, O>(propToFind: P, obj: O): O[P];
prop<P extends keyof O, O>(propToFind: P): (obj: O) => O[P];
prop<P extends string | number>(propToFind: P): <T>(obj: Record<P, T>) => T;
prop<P extends string | number, T>(propToFind: P): (obj: Record<P, T>) => T;

R.prop source

export function prop(propToFind, obj) {
  if (arguments.length === 1) return _obj => prop(propToFind, _obj)

  if (!obj) return undefined

  return obj[propToFind]
}

Tests

import {prop} from './prop'

test('prop', () => {
  expect(prop('foo')({foo: 'baz'})).toEqual('baz')

  expect(prop('bar')({foo: 'baz'})).toEqual(undefined)

  expect(prop('bar')(null)).toEqual(undefined)
})

Typescript test

import {pipe, prop} from 'rambda'

describe('R.prop', () => {
  const obj = {a: 1, b: 'foo'}
  type Something = {a?: number, b?: string}

  it('issue #553', () => {
    const result = prop('e', {e: 'test1', d: 'test2'})
    const curriedResult = prop<string>('e')({e: 'test1', d: 'test2'})

    result // $ExpectType string
    curriedResult // $ExpectType string
  })
  it('happy', () => {
    const result = prop('a', obj)

    result // $ExpectType number
  })
  it('curried', () => {
    const result = prop('b')(obj)

    result // $ExpectType string
  })
  it('curried with explicit object type', () => {
    const result = prop<'a', Something>('a')(obj)

    result // $ExpectType number | undefined
  })
  it('curried with implicit object type', () => {
    const result = pipe((value) => value as Something, prop('b'))(obj)

    result // $ExpectType string | undefined
  })
  it('curried with explicit result type', () => {
    const result = prop<'b', string>('b')(obj)

    result // $ExpectType string
  })
})

describe('with number as prop', () => {
  const list = [1, 2, 3]
  const index = 1
  it('happy', () => {
    const result = prop(index, list)

    result // $ExpectType number
  })
  it('curried require explicit type', () => {
    const result = prop<number>(index)(list)

    result // $ExpectType number
  })
})

Rambda is faster than Ramda with 87.95%

const R = require('../../dist/rambda.js')

const obj = {
  a: {c: 2},
  b: 1,
}
const propInput = 'b'

const prop = [
  {
    label: 'Rambda',
    fn: () => {
      R.prop(propInput, obj)
      R.prop(propInput)(obj)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.prop(propInput, obj)
      Ramda.prop(propInput)(obj)
    },
  },
]

propEq

propEq<K extends string | number>(propToFind: K, valueToMatch: any, obj: Record<K, any>): boolean

It returns true if obj has property propToFind and its value is equal to valueToMatch.

const obj = { foo: 'bar' }
const secondObj = { foo: 1 }

const propToFind = 'foo'
const valueToMatch = 'bar'

const result = [
  R.propEq(propToFind, valueToMatch, obj),
  R.propEq(propToFind, valueToMatch, secondObj)
]
// => [true, false]

Try this R.propEq example in Rambda REPL

All Typescript definitions

propEq<K extends string | number>(propToFind: K, valueToMatch: any, obj: Record<K, any>): boolean;
propEq<K extends string | number>(propToFind: K, valueToMatch: any): (obj: Record<K, any>) => boolean;
propEq<K extends string | number>(propToFind: K): {
  (valueToMatch: any, obj: Record<K, any>): boolean;
  (valueToMatch: any): (obj: Record<K, any>) => boolean;
};

R.propEq source

import {curry} from './curry'

function propEqFn(propToFind, valueToMatch, obj) {
  if (!obj) return false

  return obj[propToFind] === valueToMatch
}

export const propEq = curry(propEqFn)

Tests

import {propEq} from './propEq'

test('happy', () => {
  expect(propEq('foo', 'bar')({foo: 'bar'})).toBeTrue()
  expect(propEq('foo', 'bar')({foo: 'baz'})).toBeFalse()
  expect(propEq('foo')('bar')({foo: 'baz'})).toBeFalse()
  expect(propEq('foo', 'bar', null)).toBeFalse()
})

Typescript test

import {propEq} from 'rambda'

const property = 'foo'
const numberProperty = 1
const value = 'bar'
const obj = {[property]: value}
const objWithNumberIndex = {[numberProperty]: value}

describe('R.propEq', () => {
  it('happy', () => {
    const result = propEq(property, value, obj)
    result // $ExpectType boolean
  })

  it('number is property', () => {
    const result = propEq(1, value, objWithNumberIndex)
    result // $ExpectType boolean
  })

  it('with optional property', () => {
    interface MyType {
      optional?: string | number
    }

    const myObject: MyType = {}
    const valueToFind = '1111'
    // $ExpectError
    propEq('optional', valueToFind, myObject)

    // $ExpectError
    propEq('optional', valueToFind, myObject)
  })

  it('imported from @types/ramda', () => {
    interface A {
      foo: string | null
    }
    const obj: A = {
      foo: 'bar',
    }
    const value = ''
    const result = propEq('foo', value)(obj)
    result // $ExpectType boolean

    // $ExpectError
    propEq('bar', value)(obj)
  })
})

Rambda is faster than Ramda with 91.92%

const R = require('../../dist/rambda.js')

const obj = {
  a: {c: 2},
  b: 1,
}
const propInput = 'b'
const expected = {c: 2}

const propEq = [
  {
    label: 'Rambda',
    fn: () => {
      R.propEq('a')(expected)(obj)

      R.propEq('a', expected)(obj)

      R.propEq('a', expected, obj)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.propEq('a')(expected)(obj)

      Ramda.propEq('a', expected)(obj)

      Ramda.propEq('a', expected, obj)
    },
  },
]

propIs

propIs<C extends (...args: any[]) => any, K extends keyof any>(type: C, name: K, obj: any): obj is Record<K, ReturnType<C>>

It returns true if property of obj is from target type.

const obj = {a:1, b: 'foo'}

const result = [
  R.propIs(Number, 'a', obj),
  R.propIs(String, 'b', obj),
  R.propIs(Number, 'b', obj),
]
// => [true, true, false]

Try this R.propIs example in Rambda REPL

All Typescript definitions

propIs<C extends (...args: any[]) => any, K extends keyof any>(type: C, name: K, obj: any): obj is Record<K, ReturnType<C>>;
propIs<C extends new (...args: any[]) => any, K extends keyof any>(type: C, name: K, obj: any): obj is Record<K, InstanceType<C>>;
propIs<C extends (...args: any[]) => any, K extends keyof any>(type: C, name: K): (obj: any) => obj is Record<K, ReturnType<C>>;
propIs<C extends new (...args: any[]) => any, K extends keyof any>(type: C, name: K): (obj: any) => obj is Record<K, InstanceType<C>>;
propIs<C extends (...args: any[]) => any>(type: C): {
    <K extends keyof any>(name: K, obj: any): obj is Record<K, ReturnType<C>>;
    <K extends keyof any>(name: K): (obj: any) => obj is Record<K, ReturnType<C>>;
};
propIs<C extends new (...args: any[]) => any>(type: C): {
    <K extends keyof any>(name: K, obj: any): obj is Record<K, InstanceType<C>>;
    <K extends keyof any>(name: K): (obj: any) => obj is Record<K, InstanceType<C>>;
};

R.propIs source

import {curry} from './curry'
import {is} from './is'

function propIsFn(targetPrototype, property, obj) {
  return is(targetPrototype, obj[property])
}

export const propIs = curry(propIsFn)

Tests

import {propIs} from './propIs'

const obj = {a: 1, b: 'foo'}

test('when true', () => {
  expect(propIs(Number, 'a', obj)).toBeTrue()
  expect(propIs(String, 'b', obj)).toBeTrue()
})

test('when false', () => {
  expect(propIs(String, 'a', obj)).toBeFalse()
  expect(propIs(Number, 'b', obj)).toBeFalse()
})

Typescript test

import {propIs} from 'rambda'

const property = 'a'
const obj = {a: 1}

describe('R.propIs', () => {
  it('happy', () => {
    const result = propIs(Number, property, obj)
    result // $ExpectType boolean
  })

  it('curried', () => {
    const result = propIs(Number, property)(obj)
    result // $ExpectType boolean
  })
})

propOr

propOr<T, P extends string>(defaultValue: T, property: P, obj: Partial<Record<P, T>> | undefined): T

It returns either defaultValue or the value of property in obj.

const obj = {a: 1}
const defaultValue = 'DEFAULT_VALUE'
const property = 'a'

const result = [
  R.propOr(defaultValue, property, obj),
  R.propOr(defaultValue, 'foo', obj)
]
// => [1, 'DEFAULT_VALUE']

Try this R.propOr example in Rambda REPL

All Typescript definitions

propOr<T, P extends string>(defaultValue: T, property: P, obj: Partial<Record<P, T>> | undefined): T;
propOr<T, P extends string>(defaultValue: T, property: P): (obj: Partial<Record<P, T>> | undefined) => T;
propOr<T>(defaultValue: T): {
  <P extends string>(property: P, obj: Partial<Record<P, T>> | undefined): T;
  <P extends string>(property: P): (obj: Partial<Record<P, T>> | undefined) => T;
}

R.propOr source

import {curry} from './curry'
import {defaultTo} from './defaultTo'

function propOrFn(defaultValue, property, obj) {
  if (!obj) return defaultValue

  return defaultTo(defaultValue, obj[property])
}

export const propOr = curry(propOrFn)

Tests

import {propOr} from './propOr'

test('propOr (result)', () => {
  const obj = {a: 1}
  expect(propOr('default', 'a', obj)).toEqual(1)
  expect(propOr('default', 'notExist', obj)).toEqual('default')
  expect(propOr('default', 'notExist', null)).toEqual('default')
})

test('propOr (currying)', () => {
  const obj = {a: 1}
  expect(propOr('default')('a', obj)).toEqual(1)
  expect(propOr('default', 'a')(obj)).toEqual(1)
  expect(propOr('default')('notExist', obj)).toEqual('default')
  expect(propOr('default', 'notExist')(obj)).toEqual('default')
})

Typescript test

import {propOr} from 'rambda'

const obj = {foo: 'bar'}
const property = 'foo'
const fallback = 'fallback'

describe('R.propOr', () => {
  it('happy', () => {
    const result = propOr(fallback, property, obj)
    result // $ExpectType string
  })
  it('curry 1', () => {
    const result = propOr(fallback)(property, obj)
    result // $ExpectType string
  })
  it('curry 2', () => {
    const result = propOr(fallback, property)(obj)
    result // $ExpectType string
  })
  it('curry 3', () => {
    const result = propOr(fallback)(property)(obj)
    result // $ExpectType string
  })
})

props

props<P extends string, T>(propsToPick: P[], obj: Record<P, T>): T[]

It takes list with properties propsToPick and returns a list with property values in obj.

const result = R.props(
  ['a', 'b'], 
  {a:1, c:3}
)
// => [1, undefined]

Try this R.props example in Rambda REPL

All Typescript definitions

props<P extends string, T>(propsToPick: P[], obj: Record<P, T>): T[];
props<P extends string>(propsToPick: P[]): <T>(obj: Record<P, T>) => T[];
props<P extends string, T>(propsToPick: P[]): (obj: Record<P, T>) => T[];

R.props source

import {_isArray} from './_internals/_isArray'
import {mapArray} from './map'

export function props(propsToPick, obj) {
  if (arguments.length === 1) {
    return _obj => props(propsToPick, _obj)
  }
  if (!_isArray(propsToPick)) {
    throw new Error('propsToPick is not a list')
  }

  return mapArray(prop => obj[prop], propsToPick)
}

Tests

import {props} from './props'

const obj = {
  a: 1,
  b: 2,
}
const propsToPick = ['a', 'c']

test('happy', () => {
  const result = props(propsToPick, obj)
  expect(result).toEqual([1, undefined])
})

test('curried', () => {
  const result = props(propsToPick)(obj)
  expect(result).toEqual([1, undefined])
})

test('wrong input', () => {
  expect(() => props(null)(obj)).toThrow()
})

Typescript test

import {props} from 'rambda'

const obj = {a: 1, b: 2}

describe('R.props', () => {
  it('happy', () => {
    const result = props(['a', 'b'], obj)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = props(['a', 'b'])(obj)

    result // $ExpectType number[]
  })
})

range

range(startInclusive: number, endExclusive: number): number[]

It returns list of numbers between startInclusive to endExclusive markers.

R.range(0, 5)
// => [0, 1, 2, 3, 4]

Try this R.range example in Rambda REPL

All Typescript definitions

range(startInclusive: number, endExclusive: number): number[];
range(startInclusive: number): (endExclusive: number) => number[];

R.range source

export function range(start, end) {
  if (arguments.length === 1) return _end => range(start, _end)

  if (Number.isNaN(Number(start)) || Number.isNaN(Number(end))) {
    throw new TypeError('Both arguments to range must be numbers')
  }

  if (end < start) return []

  const len = end - start
  const willReturn = Array(len)

  for (let i = 0; i < len; i++) {
    willReturn[i] = start + i
  }

  return willReturn
}

Tests

import {range} from './range'

test('happy', () => {
  expect(range(0, 10)).toEqual([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
})

test('end range is bigger than start range', () => {
  expect(range(7, 3)).toEqual([])
  expect(range(5, 5)).toEqual([])
})

test('with bad input', () => {
  const throwMessage = 'Both arguments to range must be numbers'
  expect(() => range('a', 6)).toThrowWithMessage(Error, throwMessage)
  expect(() => range(6, 'z')).toThrowWithMessage(Error, throwMessage)
})

test('curry', () => {
  expect(range(0)(10)).toEqual([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
})

Typescript test

import {range} from 'rambda'

describe('R.range', () => {
  it('happy', () => {
    const result = range(1, 4)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = range(1)(4)

    result // $ExpectType number[]
  })
})

Rambda is fastest. Ramda is 61.8% slower and Lodash is 57.44% slower

const R = require('../../dist/rambda.js')

const start = 12
const end = 22
const range = [
  {
    label: 'Rambda',
    fn: () => {
      R.range(start, end)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.range(start, end)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.range(start, end)
    },
  },
]

reduce

reduce<T, TResult>(reducer: (prev: TResult, current: T, i: number) => TResult, initialValue: TResult, list: T[]): TResult

💥 It passes index of the list as third argument to reducer function.

const list = [1, 2, 3]
const initialValue = 10
const reducer = (prev, current) => prev * current

const result = R.reduce(reducer, initialValue, list)
// => 60

Try this R.reduce example in Rambda REPL

All Typescript definitions

reduce<T, TResult>(reducer: (prev: TResult, current: T, i: number) => TResult, initialValue: TResult, list: T[]): TResult;
reduce<T, TResult>(reducer: (prev: TResult, current: T) => TResult, initialValue: TResult, list: T[]): TResult;
reduce<T, TResult>(reducer: (prev: TResult, current: T, i?: number) => TResult): (initialValue: TResult, list: T[]) => TResult;
reduce<T, TResult>(reducer: (prev: TResult, current: T, i?: number) => TResult, initialValue: TResult): (list: T[]) => TResult;

R.reduce source

import {_isArray} from './_internals/_isArray'
import {_keys} from './_internals/_keys'
import {curry} from './curry'

function reduceFn(reducer, acc, list) {
  if (!_isArray(list)) {
    throw new TypeError('reduce: list must be array or iterable')
  }
  let index = 0
  const len = list.length

  while (index < len) {
    acc = reducer(acc, list[index], index, list)
    index++
  }

  return acc
}

export const reduce = curry(reduceFn)

Tests

import {reduce} from './reduce'

const reducer = (prev, current, i) => {
  expect(i).toBeNumber()

  return prev + current
}
const initialValue = 1
const list = [1, 2, 3]
const ERROR = 'reduce: list must be array or iterable'

test('happy', () => {
  expect(reduce(reducer, initialValue, list)).toEqual(7)
})

test('with object as iterable', () => {
  expect(() =>
    reduce(reducer, initialValue, {
      a: 1,
      b: 2,
    })
  ).toThrowWithMessage(TypeError, ERROR)
})

test('with undefined as iterable', () => {
  expect(() => reduce(reducer, 0, null)).toThrowWithMessage(TypeError, ERROR)
})

Typescript test

import {reduce} from 'rambda'

describe('R.reduce', () => {
  it('happy', () => {
    const result = reduce<number, number>(
      (acc, elem) => {
        acc // $ExpectType number
        elem // $ExpectType number
        return acc + elem
      },
      1,
      [1, 2, 3]
    )

    result // $ExpectType number
  })

  it('with two types', () => {
    const result = reduce<number, string>(
      (acc, elem) => {
        acc // $ExpectType string
        elem // $ExpectType number

        return `${acc}${elem}`
      },
      'foo',
      [1, 2, 3]
    )

    result // $ExpectType string
  })

  it('with index', () => {
    const result = reduce<number, number>(
      (acc, elem, i) => {
        acc // $ExpectType number
        elem // $ExpectType number
        i // $ExpectType number
        return acc + elem
      },
      1,
      [1, 2, 3]
    )

    result // $ExpectType number
  })

  it('fallback', () => {
    const result = reduce(
      (acc, val) => {
        acc // $ExpectType number
        return acc + val
      },
      1,
      [1, 2, 3]
    )

    result // $ExpectType number
  })

  it('fallback with index', () => {
    const result = reduce(
      (acc, val, i) => {
        acc // $ExpectType number
        i // $ExpectType number
        return acc + val
      },
      1,
      [1, 2, 3]
    )

    result // $ExpectType number
  })

  it('fallback with two types', () => {
    const result = reduce(
      (acc, val) => {
        acc // $ExpectType string
        return acc + val
      },
      'foo',
      [1, 2, 3]
    )

    result // $ExpectType string
  })
})

Lodash is fastest. Rambda is 60.48% slower and Ramda is 77.1% slower

const R = require('../../dist/rambda.js')

const fn = (acc, value) => acc + value
const holder = [1, 2, 3]
const acc = ''

const reduce = [
  {
    label: 'Rambda',
    fn: () => {
      R.reduce(fn, acc, holder)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.reduce(fn, acc, holder)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.reduce(holder, fn, acc)
    },
  },
]

reject

reject<T>(predicate: Predicate<T>, list: T[]): T[]

It has the opposite effect of R.filter.

const list = [1, 2, 3, 4]
const obj = {a: 1, b: 2}
const predicate = x => x > 1

const result = [
  R.reject(predicate, list),
  R.reject(predicate, obj)
]
// => [[1], {a: 1}]

Try this R.reject example in Rambda REPL

All Typescript definitions

reject<T>(predicate: Predicate<T>, list: T[]): T[];
reject<T>(predicate: Predicate<T>): (list: T[]) => T[];
reject<T>(predicate: Predicate<T>, obj: Dictionary<T>): Dictionary<T>;
reject<T, U>(predicate: Predicate<T>): (obj: Dictionary<T>) => Dictionary<T>;

R.reject source

import {filter} from './filter'

export function reject(predicate, list) {
  if (arguments.length === 1) return _list => reject(predicate, _list)

  return filter(x => !predicate(x), list)
}

Tests

import {reject} from './reject'

const isOdd = n => n % 2 === 1

test('with array', () => {
  expect(reject(isOdd)([1, 2, 3, 4])).toEqual([2, 4])
})

test('with object', () => {
  const obj = {
    a: 1,
    b: 2,
    c: 3,
    d: 4,
  }
  expect(reject(isOdd, obj)).toEqual({
    b: 2,
    d: 4,
  })
})

Typescript test

import {reject} from 'rambda'

describe('R.reject with array', () => {
  it('happy', () => {
    const result = reject(
      x => {
        x // $ExpectType number
        return x > 1
      },
      [1, 2, 3]
    )
    result // $ExpectType number[]
  })
  it('curried require explicit type', () => {
    const result = reject<number>(x => {
      x // $ExpectType number
      return x > 1
    })([1, 2, 3])
    result // $ExpectType number[]
  })
})

describe('R.reject with objects', () => {
  it('happy', () => {
    const result = reject(
      x => {
        x // $ExpectType number

        return x > 1
      },
      {a: 1, b: 2}
    )
    result // $ExpectType Dictionary<number>
  })
  it('curried require dummy type', () => {
    const result = reject<number, any>(x => {
      return x > 1
    })({a: 1, b: 2})
    result // $ExpectType Dictionary<number>
  })
})

repeat

repeat<T>(x: T): (timesToRepeat: number) => T[]

R.repeat('foo', 3)
// => ['foo', 'foo', 'foo']

Try this R.repeat example in Rambda REPL

All Typescript definitions

repeat<T>(x: T): (timesToRepeat: number) => T[];
repeat<T>(x: T, timesToRepeat: number): T[];

R.repeat source

export function repeat(x, timesToRepeat) {
  if (arguments.length === 1) {
    return _timesToRepeat => repeat(x, _timesToRepeat)
  }

  return Array(timesToRepeat).fill(x)
}

Tests

import {repeat} from './repeat'

test('repeat', () => {
  expect(repeat('')(3)).toEqual(['', '', ''])
  expect(repeat('foo', 3)).toEqual(['foo', 'foo', 'foo'])

  const obj = {}
  const arr = repeat(obj, 3)

  expect(arr).toEqual([{}, {}, {}])

  expect(arr[0] === arr[1]).toBeTrue()
})

Typescript test

import {repeat} from 'rambda'

describe('R.repeat', () => {
  it('happy', () => {
    const result = repeat(4, 7)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = repeat(4)(7)

    result // $ExpectType number[]
  })
})

Lodash is fastest. Rambda is 48.57% slower and Ramda is 68.98% slower

const R = require('../../dist/rambda.js')

const num = 10
const str = 'foo'

const repeat = [
  {
    label: 'Rambda',
    fn: () => {
      R.repeat(str, num)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.repeat(str, num)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.repeat(str, num)
    },
  },
]

replace

replace(strOrRegex: RegExp | string, replacer: string, str: string): string

It replaces strOrRegex found in str with replacer.

const strOrRegex = /o/g

const result = R.replace(strOrRegex, '|0|', 'foo')
// => 'f|0||0|'

Try this R.replace example in Rambda REPL

All Typescript definitions

replace(strOrRegex: RegExp | string, replacer: string, str: string): string;
replace(strOrRegex: RegExp | string, replacer: string): (str: string) => string;
replace(strOrRegex: RegExp | string): (replacer: string) => (str: string) => string;

R.replace source

import {curry} from './curry'

function replaceFn(pattern, replacer, str) {
  return str.replace(pattern, replacer)
}

export const replace = curry(replaceFn)

Tests

import {replace} from './replace'

test('happy', () => {
  expect(replace('foo', 'yes', 'foo bar baz')).toEqual('yes bar baz')
})

test('1', () => {
  expect(replace(/\s/g)('|')('foo bar baz')).toEqual('foo|bar|baz')
})

test('2', () => {
  expect(replace(/\s/g)('|', 'foo bar baz')).toEqual('foo|bar|baz')
})

test('3', () => {
  expect(replace(/\s/g, '|')('foo bar baz')).toEqual('foo|bar|baz')
})

Typescript test

import {replace} from 'rambda'

const str = 'foo bar foo'
const replacer = 'bar'

describe('R.replace', () => {
  it('happy', () => {
    const result = replace(/foo/g, replacer, str)

    result // $ExpectType string
  })
  it('with string as search pattern', () => {
    const result = replace('foo', replacer, str)

    result // $ExpectType string
  })
})

describe('R.replace - curried', () => {
  it('happy', () => {
    const result = replace(/foo/g, replacer)(str)

    result // $ExpectType string
  })
  it('with string as search pattern', () => {
    const result = replace('foo', replacer)(str)

    result // $ExpectType string
  })
})

Lodash is fastest. Rambda is 33.45% slower and Ramda is 33.99% slower

const R = require('../../dist/rambda.js')

const replace = [
  {
    label: 'Rambda',
    fn: () => {
      R.replace(/\s/g, '|', 'foo bar baz')
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.replace(/\s/g, '|', 'foo bar baz')
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.replace('foo bar baz', /\s/g, '|')
    },
  },
]

reverse

reverse<T>(input: T[]): T[]

It returns a reversed copy of list or string input.

const result = [
  R.reverse('foo'),
  R.reverse([1, 2, 3])
]
// => ['oof', [3, 2, 1]

Try this R.reverse example in Rambda REPL

All Typescript definitions

reverse<T>(input: T[]): T[];
reverse(input: string): string;

R.reverse source

export function reverse(listOrString) {
  if (typeof listOrString === 'string') {
    return listOrString.split('').reverse().join('')
  }

  const clone = listOrString.slice()

  return clone.reverse()
}

Tests

import {reverse} from './reverse'

test('happy', () => {
  expect(reverse([1, 2, 3])).toEqual([3, 2, 1])
})

test('with string', () => {
  expect(reverse('baz')).toEqual('zab')
})

test("it doesn't mutate", () => {
  const arr = [1, 2, 3]

  expect(reverse(arr)).toEqual([3, 2, 1])

  expect(arr).toEqual([1, 2, 3])
})

Typescript test

import {reverse} from 'rambda'

const list = [1, 2, 3, 4, 5]

describe('R.reverse', () => {
  it('happy', () => {
    const result = reverse(list)
    result // $ExpectType number[]
  })
})

set

set<T, U>(lens: Lens, replacer: U, obj: T): T

It returns a copied Object or Array with modified lens focus set to replacer value.

const input = {x: 1, y: 2}
const xLens = R.lensProp('x')

const result = [
  R.set(xLens, 4, input),
  R.set(xLens, 8, input) 
]
// => [{x: 4, y: 2}, {x: 8, y: 2}]

Try this R.set example in Rambda REPL

All Typescript definitions

set<T, U>(lens: Lens, replacer: U, obj: T): T;
set<U>(lens: Lens, replacer: U): <T>(obj: T) => T;
set(lens: Lens): <T, U>(replacer: U, obj: T) => T;

R.set source

import {always} from './always'
import {curry} from './curry'
import {over} from './over'

function setFn(lens, replacer, x) {
  return over(lens, always(replacer), x)
}

export const set = curry(setFn)

Tests

import {assoc} from './assoc'
import {lens} from './lens'
import {lensIndex} from './lensIndex'
import {lensPath} from './lensPath'
import {prop} from './prop'
import {set} from './set'

const testObject = {
  foo: 'bar',
  baz: {
    a: 'x',
    b: 'y',
  },
}

test('assoc lens', () => {
  const assocLens = lens(prop('foo'), assoc('foo'))
  const result = set(assocLens, 'FOO', testObject)
  const expected = {
    ...testObject,
    foo: 'FOO',
  }
  expect(result).toEqual(expected)
})

test('path lens', () => {
  const pathLens = lensPath('baz.a')
  const result = set(pathLens, 'z', testObject)
  const expected = {
    ...testObject,
    baz: {
      a: 'z',
      b: 'y',
    },
  }
  expect(result).toEqual(expected)
})

test('index lens', () => {
  const indexLens = lensIndex(0)

  const result = set(indexLens, 3, [1, 2])
  expect(result).toEqual([3, 2])
})

Rambda is faster than Ramda with 50.35%

const R = require('../../dist/rambda.js')

const testObj = {a: 1}

const last = [
  {
    label: 'Rambda',
    fn: () => {
      R.set(R.lensProp('a'), 2, testObj)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.set(Ramda.lensProp('a'), 2, testObj)
    },
  },
]

slice

slice(from: number, to: number, input: string): string

const list = [0, 1, 2, 3, 4, 5]
const str = 'FOO_BAR'
const from = 1
const to = 4

const result = [
  R.slice(from, to, str),
  R.slice(from, to, list)
]
// => ['OO_', [1, 2, 3]]

Try this R.slice example in Rambda REPL

All Typescript definitions

slice(from: number, to: number, input: string): string;
slice<T>(from: number, to: number, input: T[]): T[];
slice(from: number, to: number): {
  (input: string): string;
  <T>(input: T[]): T[];
};
slice(from: number): {
  (to: number, input: string): string;
  <T>(to: number, input: T[]): T[];
};

R.slice source

import {curry} from './curry'

function sliceFn(from, to, list) {
  return list.slice(from, to)
}

export const slice = curry(sliceFn)

Tests

import {slice} from './slice'

test('slice', () => {
  expect(slice(1, 3, ['a', 'b', 'c', 'd'])).toEqual(['b', 'c'])
  expect(slice(1, Infinity, ['a', 'b', 'c', 'd'])).toEqual(['b', 'c', 'd'])
  expect(slice(0, -1, ['a', 'b', 'c', 'd'])).toEqual(['a', 'b', 'c'])
  expect(slice(-3, -1, ['a', 'b', 'c', 'd'])).toEqual(['b', 'c'])
  expect(slice(0, 3, 'ramda')).toEqual('ram')
})

Typescript test

import {slice} from 'rambda'

const list = [1, 2, 3, 4, 5]

describe('R.slice', () => {
  it('happy', () => {
    const result = slice(1, 3, list)
    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = slice(1, 3)(list)
    result // $ExpectType number[]
  })
})

sort

sort<T>(sortFn: (a: T, b: T) => number, list: T[]): T[]

It returns copy of list sorted by sortFn function, where sortFn needs to return only -1, 0 or 1.

const list = [
  {a: 2},
  {a: 3},
  {a: 1}
]
const sortFn = (x, y) => {
  return x.a > y.a ? 1 : -1
}

const result = R.sort(sortFn, list)
const expected = [
  {a: 1},
  {a: 2},
  {a: 3}
]
// => `result` is equal to `expected`

Try this R.sort example in Rambda REPL

All Typescript definitions

sort<T>(sortFn: (a: T, b: T) => number, list: T[]): T[];
sort<T>(sortFn: (a: T, b: T) => number): (list: T[]) => T[];

R.sort source

import {cloneList} from './_internals/cloneList'

export function sort(sortFn, list) {
  if (arguments.length === 1) return _list => sort(sortFn, _list)

  return cloneList(list).sort(sortFn)
}

Tests

import {sort} from './sort'

const fn = (a, b) => (a > b ? 1 : -1)

test('sort', () => {
  expect(sort((a, b) => a - b)([2, 3, 1])).toEqual([1, 2, 3])
})

test("it doesn't mutate", () => {
  const list = ['foo', 'bar', 'baz']

  expect(sort(fn, list)).toEqual(['bar', 'baz', 'foo'])

  expect(list[0]).toBe('foo')
  expect(list[1]).toBe('bar')
  expect(list[2]).toBe('baz')
})

Typescript test

import {sort} from 'rambda'

const list = [3, 0, 5, 2, 1]

function sortFn(a: number, b: number): number {
  return a > b ? 1 : -1
}

describe('R.sort', () => {
  it('happy', () => {
    const result = sort(sortFn, list)
    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = sort(sortFn)(list)
    result // $ExpectType number[]
  })
})

Rambda is faster than Ramda with 40.23%

const R = require('../../dist/rambda.js')

const list = ['foo', 'bar', 'baz']
const fn = (a, b) => (a > b ? -1 : 1)

const replace = [
  {
    label: 'Rambda',
    fn: () => {
      R.sort(fn, list)
      R.sort(fn)(list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.sort(fn, list)
      Ramda.sort(fn)(list)
    },
  },
]

sortBy

sortBy<T>(sortFn: (a: T) => Ord, list: T[]): T[]

It returns copy of list sorted by sortFn function, where sortFn function returns a value to compare, i.e. it doesn't need to return only -1, 0 or 1.

const list = [
  {a: 2},
  {a: 3},
  {a: 1}
]
const sortFn = x => x.a

const result = R.sortBy(sortFn, list)
const expected = [
  {a: 1},
  {a: 2},
  {a: 3}
]
// => `result` is equal to `expected`

Try this R.sortBy example in Rambda REPL

All Typescript definitions

sortBy<T>(sortFn: (a: T) => Ord, list: T[]): T[];
sortBy<T>(sortFn: (a: T) => Ord): (list: T[]) => T[];
sortBy(sortFn: (a: any) => Ord): <T>(list: T[]) => T[];

R.sortBy source

import {cloneList} from './_internals/cloneList'

export function sortBy(sortFn, list) {
  if (arguments.length === 1) return _list => sortBy(sortFn, _list)

  const clone = cloneList(list)

  return clone.sort((a, b) => {
    const aSortResult = sortFn(a)
    const bSortResult = sortFn(b)

    if (aSortResult === bSortResult) return 0

    return aSortResult < bSortResult ? -1 : 1
  })
}

Tests

import {compose} from './compose'
import {prop} from './prop'
import {sortBy} from './sortBy'
import {toLower} from './toLower'

test('happy', () => {
  const input = [{a: 2}, {a: 1}, {a: 1}, {a: 3}]
  const expected = [{a: 1}, {a: 1}, {a: 2}, {a: 3}]

  const result = sortBy(x => x.a)(input)
  expect(result).toEqual(expected)
})

test('with compose', () => {
  const alice = {
    name: 'ALICE',
    age: 101,
  }
  const bob = {
    name: 'Bob',
    age: -10,
  }
  const clara = {
    name: 'clara',
    age: 314.159,
  }
  const people = [clara, bob, alice]
  const sortByNameCaseInsensitive = sortBy(compose(toLower, prop('name')))

  expect(sortByNameCaseInsensitive(people)).toEqual([alice, bob, clara])
})

Typescript test

import {sortBy, pipe} from 'rambda'

interface Input {
  a: number
}

describe('R.sortBy', () => {
  it('passing type to sort function', () => {
    function fn(x: any): number {
      return x.a
    }
    function fn2(x: Input): number {
      return x.a
    }

    const input = [{a: 2}, {a: 1}, {a: 0}]
    const result = sortBy(fn, input)
    const curriedResult = sortBy(fn2)(input)

    result // $ExpectType { a: number; }[]
    curriedResult // $ExpectType Input[]
    result[0].a // $ExpectType number
    curriedResult[0].a // $ExpectType number
  })
  it('passing type to sort function and list', () => {
    function fn(x: Input): number {
      return x.a
    }

    const input: Input[] = [{a: 2}, {a: 1}, {a: 0}]
    const result = sortBy(fn, input)
    const curriedResult = sortBy(fn)(input)

    result // $ExpectType Input[]
    curriedResult // $ExpectType Input[]
    result[0].a // $ExpectType number
  })
  it('with R.pipe', () => {
    interface Obj {
      value: number
    }
    const fn = pipe(sortBy<Obj>(x => x.value))

    const result = fn([{value: 1}, {value: 2}])
    result // $ExpectType Obj[]
  })
})

Rambda is fastest. Ramda is 25.29% slower and Lodash is 56.88% slower

const R = require('../../dist/rambda.js')

const list = [{a: 2}, {a: 1}, {a: 0}]
const fn = x => x.a

const replace = [
  {
    label: 'Rambda',
    fn: () => {
      R.sortBy(fn, list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.sortBy(fn, list)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.sortBy(list, fn)
    },
  },
]

split

split(separator: string | RegExp): (str: string) => string[]

Curried version of String.prototype.split

const str = 'foo|bar|baz'
const separator = '|'
const result = R.split(separator, str)
// => [ 'foo', 'bar', 'baz' ]

Try this R.split example in Rambda REPL

All Typescript definitions

split(separator: string | RegExp): (str: string) => string[];
split(separator: string | RegExp, str: string): string[];

R.split source

export function split(separator, str) {
  if (arguments.length === 1) return _str => split(separator, _str)

  return str.split(separator)
}

Tests

import {split} from './split'

const str = 'foo|bar|baz'
const splitChar = '|'
const expected = ['foo', 'bar', 'baz']

test('happy', () => {
  expect(split(splitChar, str)).toEqual(expected)
})

test('curried', () => {
  expect(split(splitChar)(str)).toEqual(expected)
})

Typescript test

import {split} from 'rambda'

const str = 'foo|bar|baz'
const splitChar = '|'

describe('R.split', () => {
  it('happy', () => {
    const result = split(splitChar, str)

    result // $ExpectType string[]
  })
  it('curried', () => {
    const result = split(splitChar)(str)

    result // $ExpectType string[]
  })
})

Rambda is fastest. Ramda is 55.37% slower and Lodash is 17.64% slower

const R = require('../../dist/rambda.js')

const str = 'foo|bar|baz'
const sep = '|'

const split = [
  {
    label: 'Rambda',
    fn: () => {
      R.split(sep, str)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.split(sep, str)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.split(str, sep)
    },
  },
]

splitAt

splitAt<T>(index: number, input: T[]): [T[], T[]]

It splits string or array at a given index.

const list = [ 1, 2, 3 ]
const result = R.splitAt(2, list)
// => [[ 1, 2 ], [ 3 ]]

Try this R.splitAt example in Rambda REPL

All Typescript definitions

splitAt<T>(index: number, input: T[]): [T[], T[]];
splitAt(index: number, input: string): [string, string];
splitAt(index: number): {
    <T>(input: T[]): [T[], T[]];
    (input: string): [string, string];
};

R.splitAt source

import {_isArray} from './_internals/_isArray'
import {drop} from './drop'
import {maybe} from './maybe'
import {take} from './take'

export function splitAt(index, input) {
  if (arguments.length === 1) {
    return _list => splitAt(index, _list)
  }
  if (!input) throw new TypeError(`Cannot read property 'slice' of ${input}`)

  if (!_isArray(input) && typeof input !== 'string') return [[], []]

  const correctIndex = maybe(
    index < 0,
    input.length + index < 0 ? 0 : input.length + index,
    index
  )

  return [take(correctIndex, input), drop(correctIndex, input)]
}

Tests

import {splitAt as splitAtRamda} from 'ramda'

import {splitAt} from './splitAt'

const list = [1, 2, 3]
const str = 'foo bar'

test('with array', () => {
  const result = splitAt(2, list)
  expect(result).toEqual([[1, 2], [3]])
})

test('with array - index is negative number', () => {
  const result = splitAt(-6, list)
  expect(result).toEqual([[], list])
})

test('with array - index is out of scope', () => {
  const result = splitAt(4, list)
  expect(result).toEqual([[1, 2, 3], []])
})

test('with string', () => {
  const result = splitAt(4, str)
  expect(result).toEqual(['foo ', 'bar'])
})

test('with string - index is negative number', () => {
  const result = splitAt(-2, str)
  expect(result).toEqual(['foo b', 'ar'])
})

test('with string - index is out of scope', () => {
  const result = splitAt(10, str)
  expect(result).toEqual([str, ''])
})

test('with array - index is out of scope', () => {
  const result = splitAt(4)(list)
  expect(result).toEqual([[1, 2, 3], []])
})

const badInputs = [1, true, /foo/g, {}]
const throwingBadInputs = [null, undefined]

test('with bad inputs', () => {
  throwingBadInputs.forEach(badInput => {
    expect(() => splitAt(1, badInput)).toThrowWithMessage(
      TypeError,
      `Cannot read property 'slice' of ${badInput}`
    )
    expect(() => splitAtRamda(1, badInput)).toThrowWithMessage(
      TypeError,
      `Cannot read properties of ${badInput} (reading 'slice')`
    )
  })

  badInputs.forEach(badInput => {
    const result = splitAt(1, badInput)
    const ramdaResult = splitAtRamda(1, badInput)
    expect(result).toEqual(ramdaResult)
  })
})

Typescript test

import {splitAt} from 'ramda'

const index = 1
const str = 'foo'
const list = [1, 2, 3]

describe('R.splitAt with array', () => {
  it('happy', () => {
    const result = splitAt(index, list)

    result // $ExpectType [number[], number[]]
  })
  it('curried', () => {
    const result = splitAt(index)(list)

    result // $ExpectType [number[], number[]]
  })
})

describe('R.splitAt with string', () => {
  it('happy', () => {
    const result = splitAt(index, str)

    result // $ExpectType [string, string]
  })
  it('curried', () => {
    const result = splitAt(index)(str)

    result // $ExpectType [string, string]
  })
})

splitEvery

splitEvery<T>(sliceLength: number, input: T[]): (T[])[]

It splits input into slices of sliceLength.

const result = [
  R.splitEvery(2, [1, 2, 3]), 
  R.splitEvery(3, 'foobar') 
]

const expected = [
  [[1, 2], [3]],
  ['foo', 'bar']
]
// => `result` is equal to `expected`

Try this R.splitEvery example in Rambda REPL

All Typescript definitions

splitEvery<T>(sliceLength: number, input: T[]): (T[])[];
splitEvery(sliceLength: number, input: string): string[];
splitEvery(sliceLength: number): {
  (input: string): string[];
  <T>(input: T[]): (T[])[];
};

R.splitEvery source

export function splitEvery(sliceLength, listOrString) {
  if (arguments.length === 1) {
    return _listOrString => splitEvery(sliceLength, _listOrString)
  }

  if (sliceLength < 1) {
    throw new Error(
      'First argument to splitEvery must be a positive integer'
    )
  }

  const willReturn = []
  let counter = 0

  while (counter < listOrString.length) {
    willReturn.push(listOrString.slice(counter, (counter += sliceLength)))
  }

  return willReturn
}

Tests

import {splitEvery} from './splitEvery'

test('happy', () => {
  expect(splitEvery(3, [1, 2, 3, 4, 5, 6, 7])).toEqual([
    [1, 2, 3],
    [4, 5, 6],
    [7],
  ])

  expect(splitEvery(3)('foobarbaz')).toEqual(['foo', 'bar', 'baz'])
})

test('with bad input', () => {
  expect(() =>
    expect(splitEvery(0)('foo')).toEqual(['f', 'o', 'o'])
  ).toThrowWithMessage(
    Error,
    'First argument to splitEvery must be a positive integer'
  )
})

Typescript test

import {splitEvery} from 'rambda'

const list = [1, 2, 3, 4, 5, 6, 7]

describe('R.splitEvery', () => {
  it('happy', () => {
    const result = splitEvery(3, list)

    result // $ExpectType number[][]
  })
  it('curried', () => {
    const result = splitEvery(3)(list)

    result // $ExpectType number[][]
  })
})

Rambda is faster than Ramda with 71.98%

const R = require('../../dist/rambda.js')

const list = [1, 2, 3, 4, 5, 6, 7]

const splitEvery = [
  {
    label: 'Rambda',
    fn: () => {
      R.splitEvery(3, list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.splitEvery(3, list)
    },
  },
]

splitWhen

splitWhen<T, U>(predicate: Predicate<T>, list: U[]): (U[])[]

It splits list to two arrays according to a predicate function.

The first array contains all members of list before predicate returns true.

const list = [1, 2, 1, 2]
const result = R.splitWhen(R.equals(2), list)
// => [[1], [2, 1, 2]]

Try this R.splitWhen example in Rambda REPL

All Typescript definitions

splitWhen<T, U>(predicate: Predicate<T>, list: U[]): (U[])[];
splitWhen<T>(predicate: Predicate<T>): <U>(list: U[]) => (U[])[];

R.splitWhen source

export function splitWhen(predicate, input) {
  if (arguments.length === 1) {
    return _input => splitWhen(predicate, _input)
  }
  if (!input)
    throw new TypeError(`Cannot read property 'length' of ${input}`)

  const preFound = []
  const postFound = []
  let found = false
  let counter = -1

  while (counter++ < input.length - 1) {
    if (found) {
      postFound.push(input[counter])
    } else if (predicate(input[counter])) {
      postFound.push(input[counter])
      found = true
    } else {
      preFound.push(input[counter])
    }
  }

  return [preFound, postFound]
}

Tests

import {splitWhen as splitWhenRamda} from 'ramda'

import {equals} from './equals'
import {splitWhen} from './splitWhen'

const list = [1, 2, 1, 2]

test('happy', () => {
  const result = splitWhen(equals(2), list)
  expect(result).toEqual([[1], [2, 1, 2]])
})

test('when predicate returns false', () => {
  const result = splitWhen(equals(3))(list)
  expect(result).toEqual([list, []])
})

const badInputs = [1, true, /foo/g, {}]
const throwingBadInputs = [null, undefined]

test('with bad inputs', () => {
  throwingBadInputs.forEach(badInput => {
    expect(() => splitWhen(equals(2), badInput)).toThrowWithMessage(
      TypeError,
      `Cannot read property 'length' of ${badInput}`
    )
    expect(() => splitWhenRamda(equals(2), badInput)).toThrowWithMessage(
      TypeError,
      `Cannot read properties of ${badInput} (reading 'length')`
    )
  })

  badInputs.forEach(badInput => {
    const result = splitWhen(equals(2), badInput)
    const ramdaResult = splitWhenRamda(equals(2), badInput)
    expect(result).toEqual(ramdaResult)
  })
})

Typescript test

import {splitWhen} from 'rambda'

const list = [1, 2, 1, 2]
const predicate = (x: number) => x === 2

describe('R.splitWhen', () => {
  it('happy', () => {
    const result = splitWhen(predicate, list)

    result // $ExpectType number[][]
  })
  it('curried', () => {
    const result = splitWhen(predicate)(list)

    result // $ExpectType number[][]
  })
})

startsWith

startsWith(target: string, str: string): boolean

When iterable is a string, then it behaves as String.prototype.startsWith. When iterable is a list, then it uses R.equals to determine if the target list starts in the same way as the given target.

💥 It doesn't work with arrays unlike its corresponding Ramda method.

const str = 'foo-bar'
const list = [{a:1}, {a:2}, {a:3}]

const result = [
  R.startsWith('foo', str),
  R.startsWith([{a:1}, {a:2}], list)
]
// => [true, true]

Try this R.startsWith example in Rambda REPL

All Typescript definitions

startsWith(target: string, str: string): boolean;
startsWith(target: string): (str: string) => boolean;
startsWith<T>(target: T[], list: T[]): boolean;
startsWith<T>(target: T[]): (list: T[]) => boolean;

R.startsWith source

import {equals} from './equals.js'
import {_isArray} from './_internals/_isArray.js'

export function startsWith(target, iterable) {
  if (arguments.length === 1)
    return _iterable => startsWith(target, _iterable)

  if (typeof iterable === 'string') {
    return iterable.startsWith(target)
  }
  if (!_isArray(target)) return false

  let correct = true
  const filtered = target.filter((x, index) => {
    if (!correct) return false
    const result = equals(x, iterable[index])
    if (!result) correct = false
    return result
  })

  return filtered.length === target.length
}

Tests

import {startsWith} from './startsWith'
import {possibleTargets, possibleIterables} from './endsWith.spec'
import {startsWith as startsWithRamda} from 'ramda'
import {compareCombinations} from './_internals/testUtils'

test('with string', () => {
  expect(startsWith('foo', 'foo-bar')).toBeTrue()
  expect(startsWith('baz')('foo-bar')).toBeFalse()
})

test('use R.equals with array', () => {
  const list = [{a: 1}, {a: 2}, {a: 3}]
  expect(startsWith({a: 1}, list)).toBeFalse()
  expect(startsWith([{a: 1}], list)).toBeTrue()
  expect(startsWith([{a: 1}, {a: 2}], list)).toBeTrue()
  expect(startsWith(list, list)).toBeTrue()
  expect(startsWith([{a: 2}], list)).toBeFalse()
})

describe('brute force', () => {
  compareCombinations({
    fn: startsWith,
    fnRamda: startsWithRamda,
    firstInput: possibleTargets,
    secondInput: possibleIterables,
    callback: errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        Object {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 0,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 0,
          "SHOULD_THROW": 0,
          "TOTAL_TESTS": 32,
        }
      `)
    },
  })
})

Typescript test

import {startsWith} from 'rambda'

describe('R.startsWith - array as iterable', () => {
  const target = [{a: 1}]
  const iterable = [{a: 1}, {a: 2}]
  it('happy', () => {
    const result = startsWith(target, iterable)

    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = startsWith(target)(iterable)

    result // $ExpectType boolean
  })
})

describe('R.startsWith - string as iterable', () => {
  const target = 'foo'
  const iterable = 'foo bar'
  it('happy', () => {
    const result = startsWith(target, iterable)

    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = startsWith(target)(iterable)

    result // $ExpectType boolean
  })
})

subtract

Curried version of x - y

const x = 3
const y = 1

const result = R.subtract(x, y) 
// => 2

Try this R.subtract example in Rambda REPL

sum

sum(list: number[]): number

R.sum([1, 2, 3, 4, 5]) 
// => 15

Try this R.sum example in Rambda REPL

All Typescript definitions

sum(list: number[]): number;

R.sum source

export function sum(list) {
  return list.reduce((prev, current) => prev + current, 0)
}

Tests

import {sum} from './sum'

test('happy', () => {
  expect(sum([1, 2, 3, 4, 5])).toBe(15)
})

symmetricDifference

symmetricDifference<T>(x: T[], y: T[]): T[]

It returns a merged list of x and y with all equal elements removed.

R.equals is used to determine equality.

const x = [ 1, 2, 3, 4 ]
const y = [ 3, 4, 5, 6 ]

const result = R.symmetricDifference(x, y)
// => [ 1, 2, 5, 6 ]

Try this R.symmetricDifference example in Rambda REPL

All Typescript definitions

symmetricDifference<T>(x: T[], y: T[]): T[];
symmetricDifference<T>(x: T[]): <T>(y: T[]) => T[];

R.symmetricDifference source

import {concat} from './concat'
import {filter} from './filter'
import {includes} from './includes'

export function symmetricDifference(x, y) {
  if (arguments.length === 1) {
    return _y => symmetricDifference(x, _y)
  }

  return concat(
    filter(value => !includes(value, y), x),
    filter(value => !includes(value, x), y)
  )
}

Tests

import {symmetricDifference} from './symmetricDifference'

test('symmetricDifference', () => {
  const list1 = [1, 2, 3, 4]
  const list2 = [3, 4, 5, 6]
  expect(symmetricDifference(list1)(list2)).toEqual([1, 2, 5, 6])

  expect(symmetricDifference([], [])).toEqual([])
})

test('symmetricDifference with objects', () => {
  const list1 = [{id: 1}, {id: 2}, {id: 3}, {id: 4}]
  const list2 = [{id: 3}, {id: 4}, {id: 5}, {id: 6}]
  expect(symmetricDifference(list1)(list2)).toEqual([
    {id: 1},
    {id: 2},
    {id: 5},
    {id: 6},
  ])
})

Typescript test

import {symmetricDifference} from 'rambda'

describe('R.symmetricDifference', () => {
  it('happy', () => {
    const list1 = [1, 2, 3, 4]
    const list2 = [3, 4, 5, 6]
    const result = symmetricDifference(list1, list2)

    result // $ExpectType number[]
  })

  it('curried', () => {
    const list1 = [{id: 1}, {id: 2}, {id: 3}, {id: 4}]
    const list2 = [{id: 3}, {id: 4}, {id: 5}, {id: 6}]
    const result = symmetricDifference(list1)(list2)

    result // $ExpectType { id: number; }[]
  })
})

T

T(): boolean

R.T() 
// => true

Try this R.T example in Rambda REPL

All Typescript definitions

T(): boolean;

R.T source

export function T() {
  return true
}

tail

tail<T>(input: T[]): T[]

It returns all but the first element of input.

const result = [
  R.tail([1, 2, 3]),  
  R.tail('foo') 
]
// => [[2, 3], 'oo']

Try this R.tail example in Rambda REPL

All Typescript definitions

tail<T>(input: T[]): T[];
tail(input: string): string;

R.tail source

import {drop} from './drop'

export function tail(listOrString) {
  return drop(1, listOrString)
}

Tests

import {tail} from './tail'

test('tail', () => {
  expect(tail([1, 2, 3])).toEqual([2, 3])
  expect(tail([1, 2])).toEqual([2])
  expect(tail([1])).toEqual([])
  expect(tail([])).toEqual([])

  expect(tail('abc')).toEqual('bc')
  expect(tail('ab')).toEqual('b')
  expect(tail('a')).toEqual('')
  expect(tail('')).toEqual('')
})

Typescript test

import {tail} from 'rambda'

describe('R.tail', () => {
  it('with string', () => {
    const result = tail('foo')

    result // $ExpectType string
  })
  it('with list', () => {
    const result = tail([1, 2, 3])

    result // $ExpectType number[]
  })
})

take

take<T>(howMany: number, input: T[]): T[]

It returns the first howMany elements of input.

const howMany = 2

const result = [
  R.take(howMany, [1, 2, 3]),
  R.take(howMany, 'foobar'),
]
// => [[1, 2], 'fo']

Try this R.take example in Rambda REPL

All Typescript definitions

take<T>(howMany: number, input: T[]): T[];
take(howMany: number, input: string): string;
take<T>(howMany: number): {
  <T>(input: T[]): T[];
  (input: string): string;
};

R.take source

import baseSlice from './_internals/baseSlice'

export function take(howMany, listOrString) {
  if (arguments.length === 1)
    return _listOrString => take(howMany, _listOrString)
  if (howMany < 0) return listOrString.slice()
  if (typeof listOrString === 'string') return listOrString.slice(0, howMany)

  return baseSlice(listOrString, 0, howMany)
}

Tests

import {take} from './take'

test('happy', () => {
  const arr = ['foo', 'bar', 'baz']

  expect(take(1, arr)).toEqual(['foo'])

  expect(arr).toEqual(['foo', 'bar', 'baz'])

  expect(take(2)(['foo', 'bar', 'baz'])).toEqual(['foo', 'bar'])
  expect(take(3, ['foo', 'bar', 'baz'])).toEqual(['foo', 'bar', 'baz'])
  expect(take(4, ['foo', 'bar', 'baz'])).toEqual(['foo', 'bar', 'baz'])
  expect(take(3)('rambda')).toEqual('ram')
})

test('with negative index', () => {
  expect(take(-1, [1, 2, 3])).toEqual([1, 2, 3])
  expect(take(-Infinity, [1, 2, 3])).toEqual([1, 2, 3])
})

test('with zero index', () => {
  expect(take(0, [1, 2, 3])).toEqual([])
})

Typescript test

import {take} from 'rambda'

const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2

describe('R.take - array', () => {
  it('happy', () => {
    const result = take(howMany, list)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = take(howMany)(list)

    result // $ExpectType number[]
  })
})

describe('R.take - string', () => {
  it('happy', () => {
    const result = take(howMany, str)

    result // $ExpectType string
  })
  it('curried', () => {
    const result = take(howMany)(str)

    result // $ExpectType string
  })
})

Rambda is fastest. Ramda is 91.96% slower and Lodash is 4.72% slower

const R = require('../../dist/rambda.js')

const list = [1, 2, 3, 4]
const num = 2

const take = [
  {
    label: 'Rambda',
    fn: () => {
      R.take(num, list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.take(num, list)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.take(list, num)
    },
  },
]

takeLast

takeLast<T>(howMany: number, input: T[]): T[]

It returns the last howMany elements of input.

const howMany = 2

const result = [
  R.takeLast(howMany, [1, 2, 3]),
  R.takeLast(howMany, 'foobar'),
]
// => [[2, 3], 'ar']

Try this R.takeLast example in Rambda REPL

All Typescript definitions

takeLast<T>(howMany: number, input: T[]): T[];
takeLast(howMany: number, input: string): string;
takeLast<T>(howMany: number): {
  <T>(input: T[]): T[];
  (input: string): string;
};

R.takeLast source

import baseSlice from './_internals/baseSlice'

export function takeLast(howMany, listOrString) {
  if (arguments.length === 1)
    return _listOrString => takeLast(howMany, _listOrString)

  const len = listOrString.length
  if (howMany < 0) return listOrString.slice()
  let numValue = howMany > len ? len : howMany

  if (typeof listOrString === 'string')
    return listOrString.slice(len - numValue)

  numValue = len - numValue

  return baseSlice(listOrString, numValue, len)
}

Tests

import {takeLast} from './takeLast'

test('with arrays', () => {
  expect(takeLast(1, ['foo', 'bar', 'baz'])).toEqual(['baz'])

  expect(takeLast(2)(['foo', 'bar', 'baz'])).toEqual(['bar', 'baz'])

  expect(takeLast(3, ['foo', 'bar', 'baz'])).toEqual(['foo', 'bar', 'baz'])

  expect(takeLast(4, ['foo', 'bar', 'baz'])).toEqual(['foo', 'bar', 'baz'])

  expect(takeLast(10, ['foo', 'bar', 'baz'])).toEqual(['foo', 'bar', 'baz'])
})

test('with strings', () => {
  expect(takeLast(3, 'rambda')).toEqual('bda')

  expect(takeLast(7, 'rambda')).toEqual('rambda')
})

test('with negative index', () => {
  expect(takeLast(-1, [1, 2, 3])).toEqual([1, 2, 3])
  expect(takeLast(-Infinity, [1, 2, 3])).toEqual([1, 2, 3])
})

Typescript test

import {takeLast} from 'rambda'

const list = [1, 2, 3, 4]
const str = 'foobar'
const howMany = 2

describe('R.takeLast - array', () => {
  it('happy', () => {
    const result = takeLast(howMany, list)

    result // $ExpectType number[]
  })
  it('curried', () => {
    const result = takeLast(howMany)(list)

    result // $ExpectType number[]
  })
})

describe('R.takeLast - string', () => {
  it('happy', () => {
    const result = takeLast(howMany, str)

    result // $ExpectType string
  })
  it('curried', () => {
    const result = takeLast(howMany)(str)

    result // $ExpectType string
  })
})

Rambda is fastest. Ramda is 93.39% slower and Lodash is 19.22% slower

const R = require('../../dist/rambda.js')

const list = [1, 2, 3, 4]
const num = 2

const takeLast = [
  {
    label: 'Rambda',
    fn: () => {
      R.takeLast(num, list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.takeLast(num, list)
    },
  },
  {
    label: 'Lodash',
    fn: () => {
      _.takeRight(list, num)
    },
  },
]

takeLastWhile

takeLastWhile(predicate: (x: string) => boolean, input: string): string

const result = R.takeLastWhile(
  x => x > 2,
  [1, 2, 3, 4]
)
// => [3, 4]

Try this R.takeLastWhile example in Rambda REPL

All Typescript definitions

takeLastWhile(predicate: (x: string) => boolean, input: string): string;
takeLastWhile(predicate: (x: string) => boolean): (input: string) => string;
takeLastWhile<T>(predicate: (x: T) => boolean, input: T[]): T[];
takeLastWhile<T>(predicate: (x: T) => boolean): <T>(input: T[]) => T[];

R.takeLastWhile source

import {_isArray} from './_internals/_isArray'

export function takeLastWhile(predicate, input) {
  if (arguments.length === 1) {
    return _input => takeLastWhile(predicate, _input)
  }
  if (input.length === 0) return input
  let found = false
  const toReturn = []
  let counter = input.length

  while (!found || counter === 0) {
    counter--
    if (predicate(input[counter]) === false) {
      found = true
    } else if (!found) {
      toReturn.push(input[counter])
    }
  }

  return _isArray(input) ? toReturn.reverse() : toReturn.reverse().join('')
}

Tests

import {takeLastWhile} from './takeLastWhile'
const assert = require('assert')

const list = [1, 2, 3, 4]

test('happy', () => {
  const predicate = x => x > 2
  const result = takeLastWhile(predicate, list)
  expect(result).toEqual([3, 4])
})

test('predicate is always true', () => {
  const predicate = x => x > 0
  const result = takeLastWhile(predicate)(list)
  expect(result).toEqual(list)
})

test('predicate is always false', () => {
  const predicate = x => x < 0
  const result = takeLastWhile(predicate, list)
  expect(result).toEqual([])
})

test('with string', () => {
  const result = takeLastWhile(x => x !== 'F', 'FOOBAR')
  expect(result).toEqual('OOBAR')
})

Typescript test

import {takeLastWhile} from 'rambda'

const list = [1, 2, 3]
const str = 'FOO'

describe('R.takeLastWhile', () => {
  it('with array', () => {
    const result = takeLastWhile(x => x > 1, list)

    result // $ExpectType number[]
  })
  it('with array - curried', () => {
    const result = takeLastWhile(x => x > 1, list)

    result // $ExpectType number[]
  })
  it('with string', () => {
    const result = takeLastWhile(x => x !== 'F', str)

    result // $ExpectType string
  })
  it('with string - curried', () => {
    const result = takeLastWhile(x => x !== 'F')(str)

    result // $ExpectType string
  })
})

takeWhile

const list = [1, 2, 3, 4]
const predicate = x => x < 3

const result = R.takeWhile(predicate, list)
// => [1, 2]

Try this R.takeWhile example in Rambda REPL

tap

tap<T>(fn: (x: T) => void, input: T): T

It applies function fn to input x and returns x.

One use case is debuging in the middle of R.compose.

const list = [1, 2, 3]

R.compose(
  R.map(x => x * 2)
  R.tap(console.log),
  R.filter(x => x > 1)
)(list)
// => `2` and `3` will be logged

Try this R.tap example in Rambda REPL

All Typescript definitions

tap<T>(fn: (x: T) => void, input: T): T;
tap<T>(fn: (x: T) => void): (input: T) => T;

R.tap source

export function tap(fn, x) {
  if (arguments.length === 1) return _x => tap(fn, _x)

  fn(x)

  return x
}

Tests

import {tap} from './tap'

test('tap', () => {
  let a = 1
  const sayX = x => (a = x)

  expect(tap(sayX, 100)).toEqual(100)
  expect(tap(sayX)(100)).toEqual(100)
  expect(a).toEqual(100)
})

Typescript test

import {tap, pipe} from 'rambda'

describe('R.tap', () => {
  it('happy', () => {
    pipe(
      tap(x => {
        x // $ExpectType number[]
      }),
      (x: number[]) => x.length
    )([1, 2])
  })
})

test

test(regExpression: RegExp): (str: string) => boolean

It determines whether str matches regExpression.

R.test(/^f/, 'foo')
// => true

Try this R.test example in Rambda REPL

All Typescript definitions

test(regExpression: RegExp): (str: string) => boolean;
test(regExpression: RegExp, str: string): boolean;

R.test source

export function test(pattern, str) {
  if (arguments.length === 1) return _str => test(pattern, _str)

  if (typeof pattern === 'string') {
    throw new TypeError(
      `‘test’ requires a value of type RegExp as its first argument; received "${pattern}"`
    )
  }

  return str.search(pattern) !== -1
}

Tests

import {test as testMethod} from './test'

test('happy', () => {
  expect(testMethod(/^x/, 'xyz')).toBeTrue()

  expect(testMethod(/^y/)('xyz')).toBeFalse()
})

test('throws if first argument is not regex', () => {
  expect(() => testMethod('foo', 'bar')).toThrowWithMessage(
    TypeError,
    '‘test’ requires a value of type RegExp as its first argument; received "foo"'
  )
})

Typescript test

import {test} from 'rambda'

const input = 'foo   '
const regex = /foo/

describe('R.test', () => {
  it('happy', () => {
    const result = test(regex, input)

    result // $ExpectType boolean
  })
  it('curried', () => {
    const result = test(regex)(input)

    result // $ExpectType boolean
  })
})

Rambda is faster than Ramda with 82.34%

const R = require('../../dist/rambda.js')

const test = [
  {
    label: 'Rambda',
    fn: () => {
      R.test(/\s/g, 'x y z')
      R.test(/\s/g)('x y z')
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.test(/\s/g, 'x y z')
      Ramda.test(/\s/g)('x y z')
    },
  },
]

times

times<T>(fn: (i: number) => T, howMany: number): T[]

It returns the result of applying function fn over members of range array.

The range array includes numbers between 0 and howMany(exclusive).

const fn = x => x * 2
const howMany = 5

R.times(fn, howMany)
// => [0, 2, 4, 6, 8]

Try this R.times example in Rambda REPL

All Typescript definitions

times<T>(fn: (i: number) => T, howMany: number): T[];
times<T>(fn: (i: number) => T): (howMany: number) => T[];

R.times source

import {map} from './map'
import {range} from './range'

export function times(fn, howMany) {
  if (arguments.length === 1) return _howMany => times(fn, _howMany)
  if (!Number.isInteger(howMany) || howMany < 0) {
    throw new RangeError('n must be an integer')
  }

  return map(fn, range(0, howMany))
}

Tests

import assert from 'assert'

import {identity} from './identity'
import {times} from './times'

test('happy', () => {
  const result = times(identity, 5)

  expect(result).toEqual([0, 1, 2, 3, 4])
})

test('with bad input', () => {
  assert.throws(() => {
    times(3)('cheers!')
  }, RangeError)
  assert.throws(() => {
    times(identity, -1)
  }, RangeError)
})

test('curry', () => {
  const result = times(identity)(5)

  expect(result).toEqual([0, 1, 2, 3, 4])
})

Typescript test

import {times, identity} from 'rambda'

describe('R.times', () => {
  it('happy', () => {
    const result = times(identity, 5)
    result // $ExpectType number[]
  })
})

toLower

toLower<S extends string>(str: S): Lowercase<S>

R.toLower('FOO')
// => 'foo'

Try this R.toLower example in Rambda REPL

All Typescript definitions

toLower<S extends string>(str: S): Lowercase<S>;
toLower(str: string): string;

R.toLower source

export function toLower(str) {
  return str.toLowerCase()
}

Tests

import {toLower} from './toLower'

test('toLower', () => {
  expect(toLower('FOO|BAR|BAZ')).toEqual('foo|bar|baz')
})

toPairs

toPairs<O extends object, K extends Extract<keyof O, string | number>>(obj: O): Array<{ [key in K]: [`${key}`, O[key]] }[K]>

It transforms an object to a list.

const list = {
  a : 1,
  b : 2,
  c : [ 3, 4 ],
}
const expected = [ [ 'a', 1 ], [ 'b', 2 ], [ 'c', [ 3, 4 ] ] ]

const result = R.toPairs(list)
// => `result` is equal to `expected`

Try this R.toPairs example in Rambda REPL

All Typescript definitions

toPairs<O extends object, K extends Extract<keyof O, string | number>>(obj: O): Array<{ [key in K]: [`${key}`, O[key]] }[K]>;
toPairs<S>(obj: Record<string | number, S>): Array<[string, S]>;

R.toPairs source

export function toPairs(obj) {
  return Object.entries(obj)
}

Tests

import {toPairs} from './toPairs'

const obj = {
  a: 1,
  b: 2,
  c: [3, 4],
}
const expected = [
  ['a', 1],
  ['b', 2],
  ['c', [3, 4]],
]

test('happy', () => {
  expect(toPairs(obj)).toEqual(expected)
})

Typescript test

import {toPairs} from 'rambda'

const obj = {
  a: 1,
  b: 2,
  c: [3, 4],
}

describe('R.toPairs', () => {
  it('happy', () => {
    const result = toPairs(obj)

    result // $ExpectType (["b", number] | ["a", number] | ["c", number[]])[]
  })
})

toString

toString(x: unknown): string

R.toString([1, 2]) 
// => '1,2'

Try this R.toString example in Rambda REPL

All Typescript definitions

toString(x: unknown): string;

R.toString source

export function toString(x) {
  return x.toString()
}

Tests

import {toString} from './toString'

test('happy', () => {
  expect(toString([1, 2, 3])).toEqual('1,2,3')
})

toUpper

toUpper<S extends string>(str: S): Uppercase<S>

R.toUpper('foo')
// => 'FOO'

Try this R.toUpper example in Rambda REPL

All Typescript definitions

toUpper<S extends string>(str: S): Uppercase<S>;
toUpper(str: string): string;

R.toUpper source

export function toUpper(str) {
  return str.toUpperCase()
}

Tests

import {toUpper} from './toUpper'

test('toUpper', () => {
  expect(toUpper('foo|bar|baz')).toEqual('FOO|BAR|BAZ')
})

transpose

transpose<T>(list: (T[])[]): (T[])[]

const list = [[10, 11], [20], [], [30, 31, 32]]
const expected = [[10, 20, 30], [11, 31], [32]]

const result = R.transpose(list)
// => `result` is equal to `expected`

Try this R.transpose example in Rambda REPL

All Typescript definitions

transpose<T>(list: (T[])[]): (T[])[];

R.transpose source

import {_isArray} from './_internals/_isArray'

export function transpose(array) {
  return array.reduce((acc, el) => {
    el.forEach((nestedEl, i) =>
      _isArray(acc[i]) ? acc[i].push(nestedEl) : acc.push([nestedEl])
    )

    return acc
  }, [])
}

Tests

import {transpose} from './transpose'

test('happy', () => {
  const input = [
    ['a', 1],
    ['b', 2],
    ['c', 3],
  ]

  expect(transpose(input)).toEqual([
    ['a', 'b', 'c'],
    [1, 2, 3],
  ])
})

test('when rows are shorter', () => {
  const actual = transpose([[10, 11], [20], [], [30, 31, 32]])
  const expected = [[10, 20, 30], [11, 31], [32]]
  expect(actual).toEqual(expected)
})

test('with empty array', () => {
  expect(transpose([])).toEqual([])
})

test('array with falsy values', () => {
  const actual = transpose([
    [true, false, undefined, null],
    [null, undefined, false, true],
  ])
  const expected = [
    [true, null],
    [false, undefined],
    [undefined, false],
    [null, true],
  ]
  expect(actual).toEqual(expected)
})

Typescript test

import {transpose} from 'rambda'

const input = [
  ['a', 1],
  ['b', 2],
  ['c', 3],
]

describe('R.transpose', () => {
  it('happy', () => {
    const result = transpose(input)

    result // $ExpectType (string | number)[][]
  })
})

trim

trim(str: string): string

R.trim('  foo  ') 
// => 'foo'

Try this R.trim example in Rambda REPL

All Typescript definitions

trim(str: string): string;

R.trim source

export function trim(str) {
  return str.trim()
}

Tests

import {trim} from './trim'

test('trim', () => {
  expect(trim(' foo ')).toEqual('foo')
})

tryCatch

tryCatch<T, U>(
  fn: (input: T) => U,
  fallback: U
): (input: T) => U

It returns function that runs fn in try/catch block. If there was an error, then fallback is used to return the result. Note that fn can be value or asynchronous/synchronous function(unlike Ramda where fallback can only be a synchronous function).

💥 Please check the tests of R.tryCatch to fully understand how this method works.

const fn = x => x.foo

const result = [
  R.tryCatch(fn, false)(null),
  R.tryCatch(fn, false)({foo: 'bar'})
]
// => [false, 'bar']

Try this R.tryCatch example in Rambda REPL

All Typescript definitions

tryCatch<T, U>(
  fn: (input: T) => U,
  fallback: U
): (input: T) => U;
tryCatch<T, U>(
  fn: (input: T) => U,
  fallback: (input: T) => U
): (input: T) => U;
tryCatch<T>(
  fn: (input: any) => Promise<any>,
  fallback: T
): (input: any) => Promise<T>;
tryCatch<T>(
  fn: (input: any) => Promise<any>,
  fallback: (input: any) => Promise<any>,
): (input: any) => Promise<T>;

R.tryCatch source

import {isFunction} from './isFunction'

export function tryCatch(fn, fallback) {
  if (!isFunction(fn)) {
    throw new Error(`R.tryCatch | fn '${fn}'`)
  }
  const passFallback = isFunction(fallback)

  return (...inputs) => {
    try {
      return fn(...inputs)
    } catch (e) {
      return passFallback ? fallback(e, ...inputs) : fallback
    }
  }
}

Tests

import {tryCatch as tryCatchRamda} from 'ramda'

import {compareCombinations} from './_internals/testUtils'
import {prop} from './prop'
import {tryCatch} from './tryCatch'

test('happy', () => {
  const fn = () => {
    throw new Error('foo')
  }
  const result = tryCatch(fn, () => true)()
  expect(result).toBeTrue()
})

test('when fallback is used', () => {
  const fn = x => x.x

  expect(tryCatch(fn, false)(null)).toBeFalse()
})

test('with json parse', () => {
  const good = () => JSON.parse(JSON.stringify({a: 1}))
  const bad = () => JSON.parse('a{a')

  expect(tryCatch(good, 1)()).toEqual({a: 1})
  expect(tryCatch(bad, 1)()).toBe(1)
})

test('when fallback is function', () => {
  const fn = x => x.x

  expect(tryCatch(fn, () => 1)(null)).toBe(1)
})

test('when fn is used', () => {
  const fn = prop('x')

  expect(tryCatch(fn, false)({})).toBe(undefined)
  expect(tryCatch(fn, false)({x: 1})).toBe(1)
})

test('fallback receives error object and all initial inputs', () => {
  function thrower(a, b, c) {
    void c
    throw new Error('throwerError')
  }

  function catchFn(e, a, b, c) {
    return [e.message, a, b, c].join('|')
  }

  const willThrow = tryCatch(thrower, catchFn)
  const result = willThrow('A', 'B', 'C')
  expect(result).toBe('throwerError|A|B|C')
})

test('fallback receives error object', () => {
  function throwFn() {
    throw new Error(10)
  }

  function eCatcher(e, a, b) {
    return e.message
  }

  const willThrow = tryCatch(throwFn, eCatcher)
  expect(willThrow([])).toBe('10')
  expect(willThrow([{}, {}, {}])).toBe('10')
})

const possibleFns = [
  null,
  () => 1,
  () => 0,
  () => JSON.parse('{a:1'),
  () => {
    const x = {}

    return x.x
  },
  x => x.foo,
  () => {
    throw new Error('foo')
  },
]

const possibleCatchers = [
  null,
  e => e.message.length,
  (e, ...inputs) => `${e.message.length} ${inputs.length}`,
  () => {
    throw new Error('bar')
  },
]

const possibleInputs = [null, {}, {foo: 1}]

describe('brute force', () => {
  compareCombinations({
    returnsFunctionFlag: true,
    firstInput: possibleFns,
    callback: errorsCounters => {
      expect(errorsCounters).toMatchInlineSnapshot(`
        Object {
          "ERRORS_MESSAGE_MISMATCH": 0,
          "ERRORS_TYPE_MISMATCH": 12,
          "RESULTS_MISMATCH": 0,
          "SHOULD_NOT_THROW": 0,
          "SHOULD_THROW": 7,
          "TOTAL_TESTS": 84,
        }
      `)
    },
    secondInput: possibleCatchers,
    thirdInput: possibleInputs,
    fn: tryCatch,
    fnRamda: tryCatchRamda,
  })
})

Typescript test

import {tryCatch, delay} from 'rambda'

describe('R.tryCatch', () => {
  it('synchronous', () => {
    const fn = (x: any) => x.x === 1

    const result = tryCatch(fn, false)(null)
    result // $ExpectType boolean
  })
  it('synchronous + fallback is function', () => {
    const fn = (x: any) => typeof x.x
    const fallback = (x: any) => typeof x
    const result = tryCatch<any, string>(fn, fallback)(null)
    result // $ExpectType string
  })

  it('asynchronous', async () => {
    const fn = async (input: any) => {
      return typeof JSON.parse('{a:')
    }
    const result = await tryCatch<string>(fn, 'fallback')(100)
    result // $ExpectType string
  })

  it('asynchronous + fallback is asynchronous', async () => {
    const fn = async (input: any) => {
      await delay(100)
      return JSON.parse(`{a:${input}`)
    }
    const fallback = async (input: any) => {
      await delay(100)
      return 'foo'
    }
    const result = await tryCatch<string>(fn, fallback)(100)
    result // $ExpectType string
  })
})

type

type(x: any): RambdaTypes

It accepts any input and it returns its type.

💥 NaN, Promise and Async are types specific for Rambda.

R.type(() => {}) // => 'Function'
R.type(async () => {}) // => 'Async'
R.type([]) // => 'Array'
R.type({}) // => 'Object'
R.type('foo') // => 'String'
R.type(1) // => 'Number'
R.type(true) // => 'Boolean'
R.type(null) // => 'Null'
R.type(/[A-z]/) // => 'RegExp'
R.type('foo'*1) // => 'NaN'

const delay = ms => new Promise(resolve => {
  setTimeout(function () {
    resolve()
  }, ms)
})
R.type(delay) // => 'Promise'

Try this R.type example in Rambda REPL

All Typescript definitions

type(x: any): RambdaTypes;

R.type source

export function type(input) {
  if (input === null) {
    return 'Null'
  } else if (input === undefined) {
    return 'Undefined'
  } else if (Number.isNaN(input)) {
    return 'NaN'
  }
  const typeResult = Object.prototype.toString.call(input).slice(8, -1)

  return typeResult === 'AsyncFunction' ? 'Async' : typeResult
}

Tests

import {type} from './type'
import {type as typeRamda} from 'ramda'

test('with symbol', () => {
  expect(type(Symbol())).toBe('Symbol')
})

test('with simple promise', () => {
  expect(type(Promise.resolve(1))).toBe('Promise')
})

test('with new Boolean', () => {
  expect(type(new Boolean(true))).toBe('Boolean')
})

test('with new String', () => {
  expect(type(new String('I am a String object'))).toEqual('String')
})

test('with new Number', () => {
  expect(type(new Number(1))).toBe('Number')
})

test('with error', () => {
  expect(type(Error(`foo`))).toBe('Error')
  expect(typeRamda(Error(`foo`))).toBe('Error')
})

test('with error - wrong @types/ramda test', () => {
  // @types/ramda expect the result to be 'Error' but it is not
  class ExtendedError extends Error {}
  expect(type(ExtendedError)).toBe('Function')
  expect(typeRamda(ExtendedError)).toBe('Function')
})

test('with new promise', () => {
  const delay = ms =>
    new Promise(resolve => {
      setTimeout(() => {
        resolve(ms + 110)
      }, ms)
    })

  expect(type(delay(10))).toEqual('Promise')
})

test('async function', () => {
  expect(type(async () => {})).toEqual('Async')
})

test('async arrow', () => {
  const asyncArrow = async () => {}
  expect(type(asyncArrow)).toBe('Async')
})

test('function', () => {
  const fn1 = () => {}
  const fn2 = function () {}

  function fn3() {}

  ;[() => {}, fn1, fn2, fn3].map(val => {
    expect(type(val)).toEqual('Function')
  })
})

test('object', () => {
  expect(type({})).toEqual('Object')
})

test('number', () => {
  expect(type(1)).toEqual('Number')
})

test('boolean', () => {
  expect(type(false)).toEqual('Boolean')
})

test('string', () => {
  expect(type('foo')).toEqual('String')
})

test('null', () => {
  expect(type(null)).toEqual('Null')
})

test('array', () => {
  expect(type([])).toEqual('Array')
  expect(type([1, 2, 3])).toEqual('Array')
})

test('regex', () => {
  expect(type(/\s/g)).toEqual('RegExp')
})

test('undefined', () => {
  expect(type(undefined)).toEqual('Undefined')
})

test('not a number', () => {
  expect(type(Number('s'))).toBe('NaN')
})

test('set', () => {
  const exampleSet = new Set([1, 2, 3])
  expect(type(exampleSet)).toBe('Set')
  expect(typeRamda(exampleSet)).toBe('Set')
})

test('function inside object 1', () => {
  const obj = {
    f() {
      return 4
    },
  }

  expect(type(obj.f)).toBe('Function')
  expect(typeRamda(obj.f)).toBe('Function')
})

test('function inside object 2', () => {
  const name = 'f'
  const obj = {
    [name]() {
      return 4
    },
  }
  expect(type(obj.f)).toBe('Function')
  expect(typeRamda(obj.f)).toBe('Function')
})

Typescript test

import {type} from 'rambda'

describe('R.type', () => {
  it('happy', () => {
    const result = type(4)

    result // $ExpectType RambdaTypes
  })
})

Rambda is faster than Ramda with 48.6%

const R = require('../../dist/rambda.js')

const {listOfVariousTypes} = require('./_utils')

const limit = 1000

function applyBenchmark(fn) {
  listOfVariousTypes.forEach(mode => {
    Array(limit)
      .fill(mode)
      .forEach(x => fn(x))
  })
}

const test = [
  {
    label: 'Rambda',
    fn: () => {
      applyBenchmark(R.type)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      applyBenchmark(Ramda.type)
    },
  },
]

unapply

unapply<T = any>(fn: (args: any[]) => T): (...args: any[]) => T

It calls a function fn with the list of values of the returned function.

R.unapply is the opposite of R.apply method.

R.unapply(JSON.stringify)(1, 2, 3)
//=> '[1,2,3]'

Try this R.unapply example in Rambda REPL

All Typescript definitions

unapply<T = any>(fn: (args: any[]) => T): (...args: any[]) => T;

R.unapply source

export function unapply(fn) {
  return function (...args) {
    return fn.call(this, args)
  }
}

Tests

import {apply} from './apply'
import {unapply} from './unapply'
import {identity} from './identity'
import {converge} from './converge'
import {prop} from './prop'
import {sum} from './sum'

test('happy', () => {
  const fn = unapply(identity)
  expect(fn(1, 2, 3)).toEqual([1, 2, 3])
  expect(fn()).toEqual([])
})

test('returns a function which is always passed one argument', function () {
  const fn = unapply(function () {
    return arguments.length
  })
  expect(fn('x')).toEqual(1)
  expect(fn('x', 'y')).toEqual(1)
  expect(fn('x', 'y', 'z')).toEqual(1)
})

test('forwards arguments to decorated function as an array', function () {
  const fn = unapply(function (xs) {
    return '[' + xs + ']'
  })
  expect(fn(2)).toEqual('[2]')
  expect(fn(2, 4)).toEqual('[2,4]')
  expect(fn(2, 4, 6)).toEqual('[2,4,6]')
})

test('returns a function with length 0', function () {
  const fn = unapply(identity)
  expect(fn.length).toEqual(0)
})

test('is the inverse of R.apply', function () {
  let a, b, c, d, e, f, g, n
  const rand = function () {
    return Math.floor(200 * Math.random()) - 100
  }

  f = Math.max
  g = unapply(apply(f))
  n = 1
  while (n <= 100) {
    a = rand()
    b = rand()
    c = rand()
    d = rand()
    e = rand()
    expect(f(a, b, c, d, e)).toEqual(g(a, b, c, d, e))
    n += 1
  }

  f = function (xs) {
    return '[' + xs + ']'
  }
  g = apply(unapply(f))
  n = 1
  while (n <= 100) {
    a = rand()
    b = rand()
    c = rand()
    d = rand()
    e = rand()
    expect(f([a, b, c, d, e])).toEqual(g([a, b, c, d, e]))
    n += 1
  }
})

test('it works with converge', () => {
  const fn = unapply(sum)
  const convergeFn = converge(fn, [prop('a'), prop('b'), prop('c')])
  const obj = {
    a: 1337,
    b: 42,
    c: 1,
  }
  const expected = 1337 + 42 + 1
  expect(convergeFn(obj)).toEqual(expected)
})

Typescript test

import {join, unapply, sum} from 'rambda'

describe('R.unapply', () => {
  it('happy', () => {
    const fn = unapply(sum)

    fn(1, 2, 3) // $ExpectType number
  })

  it('joins a string', () => {
    const fn = unapply(join(''))

    fn('s', 't', 'r', 'i', 'n', 'g') // $ExpectType string
  })
})

union

union<T>(x: T[], y: T[]): T[]

It takes two lists and return a new list containing a merger of both list with removed duplicates.

R.equals is used to compare for duplication.

const result = R.union([1,2,3], [3,4,5]);
// => [1, 2, 3, 4, 5]

Try this R.union example in Rambda REPL

All Typescript definitions

union<T>(x: T[], y: T[]): T[];
union<T>(x: T[]): (y: T[]) => T[];

R.union source

import {includes} from './includes'
import {cloneList} from './_internals/cloneList'

export function union(x, y) {
  if (arguments.length === 1) return _y => union(x, _y)

  const toReturn = cloneList(x)

  y.forEach(yInstance => {
    if (!includes(yInstance, x)) toReturn.push(yInstance)
  })

  return toReturn
}

Tests

import {union} from './union'

test('happy', () => {
  expect(union([1, 2], [2, 3])).toEqual([1, 2, 3])
})

test('with list of objects', () => {
  const list1 = [{a: 1}, {a: 2}]
  const list2 = [{a: 2}, {a: 3}]
  const result = union(list1)(list2)
})

Typescript test

import {union} from 'rambda'

describe('R.union', () => {
  it('happy', () => {
    const result = union([1, 2], [2, 3])

    result // $ExpectType number[]
  })
  it('with array of objects - case 1', () => {
    const list1 = [{a: 1}, {a: 2}]
    const list2 = [{a: 2}, {a: 3}]
    const result = union(list1, list2)
    result // $ExpectType { a: number; }[]
  })
  it('with array of objects - case 2', () => {
    const list1 = [{a: 1, b: 1}, {a: 2}]
    const list2 = [{a: 2}, {a: 3, b: 3}]
    const result = union(list1, list2)
    result[0].a // $ExpectType number
    result[0].b // $ExpectType number | undefined
  })
})

describe('R.union - curried', () => {
  it('happy', () => {
    const result = union([1, 2])([2, 3])

    result // $ExpectType number[]
  })
  it('with array of objects - case 1', () => {
    const list1 = [{a: 1}, {a: 2}]
    const list2 = [{a: 2}, {a: 3}]
    const result = union(list1)(list2)
    result // $ExpectType { a: number; }[]
  })
  it('with array of objects - case 2', () => {
    const list1 = [{a: 1, b: 1}, {a: 2}]
    const list2 = [{a: 2}, {a: 3, b: 3}]
    const result = union(list1)(list2)
    result[0].a // $ExpectType number
    result[0].b // $ExpectType number | undefined
  })
})

uniq

uniq<T>(list: T[]): T[]

It returns a new array containing only one copy of each element of list.

R.equals is used to determine equality.

const list = [1, 1, {a: 1}, {a: 2}, {a:1}]

R.uniq(list)
// => [1, {a: 1}, {a: 2}]

Try this R.uniq example in Rambda REPL

All Typescript definitions

uniq<T>(list: T[]): T[];

R.uniq source

import {_Set} from './_internals/set'

export function uniq(list) {
  const set = new _Set()
  const willReturn = []
  list.forEach(item => {
    if (set.checkUniqueness(item)) {
      willReturn.push(item)
    }
  })

  return willReturn
}

Tests

import {uniq} from './uniq'
import {uniq as uniqRamda} from 'ramda'

test('happy', () => {
  const list = [1, 2, 3, 3, 3, 1, 2, 0]
  expect(uniq(list)).toEqual([1, 2, 3, 0])
})

test('with object', () => {
  const list = [{a: 1}, {a: 2}, {a: 1}, {a: 2}]
  expect(uniq(list)).toEqual([{a: 1}, {a: 2}])
})

test('with nested array', () => {
  expect(uniq([[42], [42]])).toEqual([[42]])
})
test('with booleans', () => {
  expect(uniq([[false], [false], [true]])).toEqual([[false], [true]])
})

test('with falsy values', () => {
  expect(uniq([undefined, null])).toEqual([undefined, null])
})

test('can distinct between string and number', () => {
  expect(uniq([1, '1'])).toEqual([1, '1'])
})

Typescript test

import {uniq} from 'rambda'

describe('R.uniq', () => {
  it('happy', () => {
    const result = uniq([1, 2, 3, 3, 3, 1, 2, 0])
    result // $ExpectType number[]
  })
})

Rambda is faster than Ramda with 90.24%

const R = require('../../dist/rambda.js')

const {
  uniqListOfStrings,
  uniqListOfBooleans,
  uniqListOfNumbers,
  uniqListOfLists,
  uniqListOfObjects,
} = require('./_utils.js')

const limit = 100

const modes = [
  uniqListOfStrings(limit),
  uniqListOfBooleans(limit),
  uniqListOfNumbers(limit),
  uniqListOfLists(limit),
  uniqListOfObjects(limit),
]

function applyBenchmark(fn, input) {
  fn(input)
}

const tests = [
  {
    label: 'Rambda',
    fn: R.uniq,
  },
  {
    label: 'Ramda',
    fn: Ramda.uniq,
  },
]

uniqWith

uniqWith<T, U>(predicate: (x: T, y: T) => boolean, list: T[]): T[]

It returns a new array containing only one copy of each element in list according to predicate function.

This predicate should return true, if two elements are equal.

const list = [
  {id: 0, title:'foo'},
  {id: 1, title:'bar'},
  {id: 2, title:'baz'},
  {id: 3, title:'foo'},
  {id: 4, title:'bar'},
]

const expected = [
  {id: 0, title:'foo'},
  {id: 1, title:'bar'},
  {id: 2, title:'baz'},
]

const predicate = (x,y) => x.title === y.title

const result = R.uniqWith(predicate, list)
// => `result` is equal to `expected`

Try this R.uniqWith example in Rambda REPL

All Typescript definitions

uniqWith<T, U>(predicate: (x: T, y: T) => boolean, list: T[]): T[];
uniqWith<T, U>(predicate: (x: T, y: T) => boolean): (list: T[]) => T[];

R.uniqWith source

function includesWith(predicate, target, list) {
  let willReturn = false
  let index = -1

  while (++index < list.length && !willReturn) {
    const value = list[index]

    if (predicate(target, value)) {
      willReturn = true
    }
  }

  return willReturn
}

export function uniqWith(predicate, list) {
  if (arguments.length === 1) return _list => uniqWith(predicate, _list)

  let index = -1
  const willReturn = []

  while (++index < list.length) {
    const value = list[index]

    if (!includesWith(predicate, value, willReturn)) {
      willReturn.push(value)
    }
  }

  return willReturn
}

Tests

import {uniqWith} from './uniqWith'
import {uniqWith as uniqWithRamda} from 'ramda'

const list = [{a: 1}, {a: 1}]

test('happy', () => {
  const fn = (x, y) => x.a === y.a

  const result = uniqWith(fn, list)
  expect(result).toEqual([{a: 1}])
})

test('with list of strings', () => {
  const fn = (x, y) => x.length === y.length
  const list = ['0', '11', '222', '33', '4', '55']
  const result = uniqWith(fn)(list)
  const resultRamda = uniqWithRamda(fn, list)
  expect(result).toEqual(['0', '11', '222'])
  expect(resultRamda).toEqual(['0', '11', '222'])
})

Typescript test

import {uniqWith} from 'rambda'

describe('R.uniqWith', () => {
  it('happy', () => {
    const list = [{a: 1}, {a: 1}]

    const fn = (x: any, y: any) => x.a === y.a

    const result = uniqWith(fn, list)
    result // $ExpectType { a: number; }[]
  })
})

Rambda is slower than Ramda with 25.38%

const R = require('../../dist/rambda.js')

const {
  uniqListOfStrings,
  uniqListOfBooleans,
  uniqListOfNumbers,
  uniqListOfLists,
  uniqListOfObjects,
} = require('./_utils.js')

const limit = 100

const modes = [
  [uniqListOfStrings(limit), (x, y) => x.length === y.length],
  [uniqListOfBooleans(limit), (x, y) => x === y],
  [uniqListOfNumbers(limit), (x, y) => x > y],
  [uniqListOfLists(limit), (x, y) => x.length === y.length],
  [
    uniqListOfObjects(limit),
    x => (x, y) => Object.keys(x).length === Object.keys(y).length,
  ],
]

function applyBenchmark(fn, input) {
  return fn(input[1], input[0])
}

const tests = [
  {
    label: 'Rambda',
    fn: R.uniqWith,
  },
  {
    label: 'Ramda',
    fn: Ramda.uniqWith,
  },
]

unless

unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, x: T): T | U

The method returns function that will be called with argument input.

If predicate(input) returns false, then the end result will be the outcome of whenFalse(input).

In the other case, the final output will be the input itself.

const fn = R.unless(
  x => x > 2,
  x => x + 10
)

const result = [
  fn(1),
  fn(5)
]
// => [11, 5]

Try this R.unless example in Rambda REPL

All Typescript definitions

unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U, x: T): T | U;
unless<T, U>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => U): (x: T) => T | U;
unless<T>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => T, x: T): T;
unless<T>(predicate: (x: T) => boolean, whenFalseFn: (x: T) => T): (x: T) => T;

R.unless source

export function unless(predicate, whenFalse) {
  if (arguments.length === 1) {
    return _whenFalse => unless(predicate, _whenFalse)
  }

  return input => (predicate(input) ? input : whenFalse(input))
}

Tests

import {inc} from './inc'
import {isNil} from './isNil'
import {unless} from './unless'

test('happy', () => {
  const safeInc = unless(isNil, inc)
  expect(safeInc(null)).toBeNull()
  expect(safeInc(1)).toBe(2)
})

test('curried', () => {
  const safeIncCurried = unless(isNil)(inc)
  expect(safeIncCurried(null)).toBeNull()
})

Typescript test

import {unless, inc} from 'rambda'

describe('R.unless', () => {
  it('happy', () => {
    const fn = unless(x => x > 5, inc)
    const result = fn(1)
    result // $ExpectType number
  })
  it('with one explicit type', () => {
    const result = unless(
      x => {
        x // $ExpectType number
        return x > 5
      },
      x => {
        x // $ExpectType number
        return x + 1
      },
      1
    )
    result // $ExpectType number
  })
  it('with two different explicit types', () => {
    const result = unless(
      x => {
        x // $ExpectType number
        return x > 5
      },
      x => {
        x // $ExpectType number
        return `${x}-foo`
      },
      1
    )
    result // $ExpectType string | number
  })
})

describe('R.unless - curried', () => {
  it('happy', () => {
    const fn = unless(x => x > 5, inc)
    const result = fn(1)
    result // $ExpectType number
  })
  it('with one explicit type', () => {
    const fn = unless<number>(
      x => {
        x // $ExpectType number
        return x > 5
      },
      x => {
        x // $ExpectType number
        return x + 1
      }
    )
    const result = fn(1)
    result // $ExpectType number
  })
  it('with two different explicit types', () => {
    const fn = unless<number, string>(
      x => {
        x // $ExpectType number
        return x > 5
      },
      x => {
        x // $ExpectType number
        return `${x}-foo`
      }
    )
    const result = fn(1)
    result // $ExpectType string | number
  })
})

update

update<T>(index: number, newValue: T, list: T[]): T[]

It returns a copy of list with updated element at index with newValue.

const index = 2
const newValue = 88
const list = [1, 2, 3, 4, 5]

const result = R.update(index, newValue, list)
// => [1, 2, 88, 4, 5]

Try this R.update example in Rambda REPL

All Typescript definitions

update<T>(index: number, newValue: T, list: T[]): T[];
update<T>(index: number, newValue: T): (list: T[]) => T[];

R.update source

import {curry} from './curry'
import {cloneList} from './_internals/cloneList'

function updateFn(index, newValue, list) {
  const clone = cloneList(list)
  if (index === -1) return clone.fill(newValue, index)

  return clone.fill(newValue, index, index + 1)
}

export const update = curry(updateFn)

Tests

import {update} from './update'

const list = [1, 2, 3]

test('happy', () => {
  const newValue = 8
  const index = 1
  const result = update(index, newValue, list)
  const curriedResult = update(index, newValue)(list)
  const tripleCurriedResult = update(index)(newValue)(list)

  const expected = [1, 8, 3]
  expect(result).toEqual(expected)
  expect(curriedResult).toEqual(expected)
  expect(tripleCurriedResult).toEqual(expected)
})

test('list has no such index', () => {
  const newValue = 8
  const index = 10
  const result = update(index, newValue, list)

  expect(result).toEqual(list)
})

test('with negative index', () => {
  expect(update(-1, 10, [1])).toEqual([10])
  expect(update(-1, 10, [])).toEqual([])
  expect(update(-1, 10, list)).toEqual([1, 2, 10])
  expect(update(-2, 10, list)).toEqual([1, 10, 3])
  expect(update(-3, 10, list)).toEqual([10, 2, 3])
})

Typescript test

import {update} from 'rambda'

describe('R.update', () => {
  it('happy', () => {
    const result = update(1, 0, [1, 2, 3])
    result // $ExpectType number[]
  })
})

Rambda is faster than Ramda with 52.35%

const R = require('../../dist/rambda.js')

const list = [0, 1, 2]
const index = 1
const replacer = 7

const update = [
  {
    label: 'Rambda',
    fn: () => {
      R.update(replacer, index, list)
      R.update(replacer, index)(list)
      R.update(replacer)(index)(list)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.update(replacer, index, list)
      Ramda.update(replacer, index)(list)
      Ramda.update(replacer)(index)(list)
    },
  },
]

values

values<T extends object, K extends keyof T>(obj: T): T[K][]

With correct input, this is nothing more than Object.values(obj). If obj is not an object, then it returns an empty array.

const obj = {a:1, b:2}

R.values(obj)
// => [1, 2]

Try this R.values example in Rambda REPL

All Typescript definitions

values<T extends object, K extends keyof T>(obj: T): T[K][];

R.values source

import {type} from './type'

export function values(obj) {
  if (type(obj) !== 'Object') return []

  return Object.values(obj)
}

Tests

import {values} from './values'

test('happy', () => {
  expect(
    values({
      a: 1,
      b: 2,
      c: 3,
    })
  ).toEqual([1, 2, 3])
})

test('with bad input', () => {
  expect(values(null)).toEqual([])
  expect(values(undefined)).toEqual([])
  expect(values(55)).toEqual([])
  expect(values('foo')).toEqual([])
  expect(values(true)).toEqual([])
  expect(values(false)).toEqual([])
  expect(values(NaN)).toEqual([])
  expect(values(Infinity)).toEqual([])
  expect(values([])).toEqual([])
})

Typescript test

import {values} from 'rambda'

describe('R.values', () => {
  it('happy', () => {
    const result = values({
      a: 1,
      b: 2,
      c: 3,
    })
    result // $ExpectType number[]
  })
})

view

view<T, U>(lens: Lens): (target: T) => U

It returns the value of lens focus over target object.

const lens = R.lensProp('x')

R.view(lens, {x: 1, y: 2}) // => 1
R.view(lens, {x: 4, y: 2}) // => 4

Try this R.view example in Rambda REPL

All Typescript definitions

view<T, U>(lens: Lens): (target: T) => U;
view<T, U>(lens: Lens, target: T): U;

R.view source

const Const = x => ({
  x,
  map: fn => Const(x),
})

export function view(lens, target) {
  if (arguments.length === 1) return _target => view(lens, _target)

  return lens(Const)(target).x
}

Tests

import {assoc} from './assoc'
import {lens} from './lens'
import {prop} from './prop'
import {view} from './view'

const testObject = {foo: 'Led Zeppelin'}
const assocLens = lens(prop('foo'), assoc('foo'))

test('happy', () => {
  expect(view(assocLens, testObject)).toEqual('Led Zeppelin')
})

Typescript test

import {lens, view, assoc} from 'rambda'

interface Input {
  foo: string
}

const testObject: Input = {
  foo: 'Led Zeppelin',
}

const fooLens = lens<Input, string, string>((x: Input) => {
  return x.foo
}, assoc('foo'))

describe('R.view', () => {
  it('happt', () => {
    const result = view<Input, string>(fooLens, testObject)
    result // $ExpectType string
  })
})

Rambda is faster than Ramda with 76.15%

const R = require('../../dist/rambda.js')

const testObj = {a: 1}

const last = [
  {
    label: 'Rambda',
    fn: () => {
      R.view(R.lensProp('a'), testObj)
    },
  },
  {
    label: 'Ramda',
    fn: () => {
      Ramda.view(Ramda.lensProp('a'), testObj)
    },
  },
]

when

when<T, U>(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U, input: T): T | U

All Typescript definitions

when<T, U>(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U, input: T): T | U;
when<T, U>(predicate: (x: T) => boolean, whenTrueFn: (a: T) => U): (input: T) => T | U;
when<T, U>(predicate: (x: T) => boolean): ((whenTrueFn: (a: T) => U) => (input: T) => T | U);

R.when source

import {curry} from './curry'

function whenFn(predicate, whenTrueFn, input) {
  if (!predicate(input)) return input

  return whenTrueFn(input)
}

export const when = curry(whenFn)

Tests

import {add} from './add'
import {when} from './when'

const predicate = x => typeof x === 'number'

test('happy', () => {
  const fn = when(predicate, add(11))
  expect(fn(11)).toBe(22)
  expect(fn('foo')).toBe('foo')
})

Typescript test

import {when} from 'rambda'

const predicate = (x: number) => x > 2
const whenTrueFn = (x: number) => String(x)

describe('R.when', () => {
  it('happy', () => {
    const result = when(predicate, whenTrueFn, 1)
    result // $ExpectType string | 1
  })

  it('curry 1', () => {
    const fn = when(predicate, whenTrueFn)
    const result = fn(1)
    result // $ExpectType string | number
  })

  it('curry 2 require explicit types', () => {
    const fn = when<number, string>(predicate)(whenTrueFn)
    const result = fn(1)
    result // $ExpectType string | number
  })
})

where

where<T, U>(conditions: T, input: U): boolean

It returns true if all each property in conditions returns true when applied to corresponding property in input object.

const condition = R.where({
  a : x => typeof x === "string",
  b : x => x === 4
})
const input = {
  a : "foo",
  b : 4,
  c : 11,
}

const result = condition(input) 
// => true

Try this R.where example in Rambda REPL

All Typescript definitions

where<T, U>(conditions: T, input: U): boolean;
where<T>(conditions: T): <U>(input: U) => boolean;
where<ObjFunc2, U>(conditions: ObjFunc2, input: U): boolean;
where<ObjFunc2>(conditions: ObjFunc2): <U>(input: U) => boolean;

R.where source

export function where(conditions, input) {
  if (input === undefined) {
    return _input => where(conditions, _input)
  }
  let flag = true
  for (const prop in conditions) {
    const result = conditions[prop](input[prop])
    if (flag && result === false) {
      flag = false
    }
  }

  return flag
}

Tests

import {equals} from './equals'
import {where} from './where'

test('when true', () => {
  const predicate = where({
    a: equals('foo'),
    b: equals('bar'),
  })
  expect(
    predicate({
      a: 'foo',
      b: 'bar',
      x: 11,
      y: 19,
    })
  ).toEqual(true)
})

test('when false', () => {
  const predicate = where({
    a: equals('foo'),
    b: equals('baz'),
  })
  expect(
    predicate({
      a: 'foo',
      b: 'bar',
      x: 11,
      y: 19,
    })
  ).toEqual(false)
})

Typescript test

import {where, equals} from 'rambda'

describe('R.where', () => {
  it('happy', () => {
    const input = {
      a: 'foo',
      b: 'bar',
      x: 11,
      y: 19,
    }
    const conditions = {
      a: equals('foo'),
      b: equals('bar'),
    }
    const result = where(conditions, input)
    const curriedResult = where(conditions)(input)
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

whereEq

whereEq<T, U>(condition: T, input: U): boolean

It will return true if all of input object fully or partially include rule object.

R.equals is used to determine equality.

const condition = { a : { b : 1 } }
const input = {
  a : { b : 1 },
  c : 2
}

const result = whereEq(condition, input)
// => true

Try this R.whereEq example in Rambda REPL

All Typescript definitions

whereEq<T, U>(condition: T, input: U): boolean;
whereEq<T>(condition: T): <U>(input: U) => boolean;

R.whereEq source

import {equals} from './equals'
import {filter} from './filter'

export function whereEq(condition, input) {
  if (arguments.length === 1) {
    return _input => whereEq(condition, _input)
  }

  const result = filter(
    (conditionValue, conditionProp) =>
      equals(conditionValue, input[conditionProp]),
    condition
  )

  return Object.keys(result).length === Object.keys(condition).length
}

Tests

import {whereEq} from './whereEq'

test('when true', () => {
  const condition = {a: 1}
  const input = {
    a: 1,
    b: 2,
  }

  const result = whereEq(condition, input)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('when false', () => {
  const condition = {a: 1}
  const input = {b: 2}

  const result = whereEq(condition, input)
  const expectedResult = false

  expect(result).toEqual(expectedResult)
})

test('with nested object', () => {
  const condition = {a: {b: 1}}
  const input = {
    a: {b: 1},
    c: 2,
  }

  const result = whereEq(condition)(input)
  const expectedResult = true

  expect(result).toEqual(expectedResult)
})

test('with wrong input', () => {
  const condition = {a: {b: 1}}

  expect(() => whereEq(condition, null)).toThrowWithMessage(
    TypeError,
    `Cannot read properties of null (reading 'a')`
  )
})

Typescript test

import {whereEq} from 'rambda'

describe('R.whereEq', () => {
  it('happy', () => {
    const result = whereEq({a: {b: 2}}, {b: 2})
    const curriedResult = whereEq({a: {b: 2}})({b: 2})
    result // $ExpectType boolean
    curriedResult // $ExpectType boolean
  })
})

without

without<T>(matchAgainst: T[], source: T[]): T[]

It will return a new array, based on all members of source list that are not part of matchAgainst list.

R.equals is used to determine equality.

const source = [1, 2, 3, 4]
const matchAgainst = [2, 3]

const result = R.without(matchAgainst, source)
// => [1, 4]

Try this R.without example in Rambda REPL

All Typescript definitions

without<T>(matchAgainst: T[], source: T[]): T[];
without<T>(matchAgainst: T[]): (source: T[]) => T[];

R.without source

import {reduce} from './reduce'
import {_indexOf} from './equals'

export function without(matchAgainst, source) {
  if (source === undefined) {
    return _source => without(matchAgainst, _source)
  }

  return reduce(
    (prev, current) =>
      _indexOf(current, matchAgainst) > -1 ? prev : prev.concat(current),
    [],
    source
  )
}

Tests

import {without} from './without'
import {without as withoutRamda} from 'ramda'

test('should return a new list without values in the first argument', () => {
  const itemsToOmit = ['A', 'B', 'C']
  const collection = ['A', 'B', 'C', 'D', 'E', 'F']

  expect(without(itemsToOmit, collection)).toEqual(['D', 'E', 'F'])
  expect(without(itemsToOmit)(collection)).toEqual(['D', 'E', 'F'])
})

test('with list of objects', () => {
  const itemsToOmit = [{a: 1}, {c: 3}]
  const collection = [{a: 1}, {b: 2}, {c: 3}, {d: 4}]
  const expected = [{b: 2}, {d: 4}]

  expect(without(itemsToOmit, collection)).toEqual(expected)
  expect(withoutRamda(itemsToOmit, collection)).toEqual(expected)
})

test('ramda accepts string as target input while rambda throws', () => {
  expect(withoutRamda('0:1', ['0', '0:1'])).toEqual([])
  expect(() => without('0:1', ['0', '0:1'])).toThrow()
  expect(without(['0:1'], ['0', '0:1'])).toEqual(['0'])
})

test('ramda test', () => {
  expect(without([1, 2])([1, 2, 1, 3, 4])).toEqual([3, 4])
})

Typescript test

import {without} from 'rambda'

const itemsToOmit = ['A', 'B', 'C']
const collection = ['A', 'B', 'C', 'D', 'E', 'F']

describe('R.without', () => {
  it('happy', () => {
    const result = without(itemsToOmit, collection)

    result // $ExpectType string[]
  })
  it('curried', () => {
    const result = without(itemsToOmit)(collection)

    result // $ExpectType string[]
  })
})

xor

xor(x: boolean, y: boolean): boolean

Logical XOR

const result = [
  xor(true, true),
  xor(false, false),
  xor(false, true),
]
// => [false, false, true]

Try this R.xor example in Rambda REPL

All Typescript definitions

xor(x: boolean, y: boolean): boolean;
xor(y: boolean): (y: boolean) => boolean;

R.xor source

export function xor(a, b) {
  if (arguments.length === 1) return _b => xor(a, _b)

  return (Boolean(a) && !b) || (Boolean(b) && !a)
}

Tests

import {xor} from './xor'

test('compares two values with exclusive or', () => {
  expect(xor(true, true)).toEqual(false)
  expect(xor(true, false)).toEqual(true)
  expect(xor(false, true)).toEqual(true)
  expect(xor(false, false)).toEqual(false)
})

test('when both values are truthy, it should return false', () => {
  expect(xor(true, 'foo')).toEqual(false)
  expect(xor(42, true)).toEqual(false)
  expect(xor('foo', 42)).toEqual(false)
  expect(xor({}, true)).toEqual(false)
  expect(xor(true, [])).toEqual(false)
  expect(xor([], {})).toEqual(false)
  expect(xor(new Date(), true)).toEqual(false)
  expect(xor(true, Infinity)).toEqual(false)
  expect(xor(Infinity, new Date())).toEqual(false)
})

test('when both values are falsy, it should return false', () => {
  expect(xor(null, false)).toEqual(false)
  expect(xor(false, undefined)).toEqual(false)
  expect(xor(undefined, null)).toEqual(false)
  expect(xor(0, false)).toEqual(false)
  expect(xor(false, NaN)).toEqual(false)
  expect(xor(NaN, 0)).toEqual(false)
  expect(xor('', false)).toEqual(false)
})

test('when one argument is truthy and the other is falsy, it should return true', () => {
  expect(xor('foo', null)).toEqual(true)
  expect(xor(null, 'foo')).toEqual(true)
  expect(xor(undefined, 42)).toEqual(true)
  expect(xor(42, undefined)).toEqual(true)
  expect(xor(Infinity, NaN)).toEqual(true)
  expect(xor(NaN, Infinity)).toEqual(true)
  expect(xor({}, '')).toEqual(true)
  expect(xor('', {})).toEqual(true)
  expect(xor(new Date(), 0)).toEqual(true)
  expect(xor(0, new Date())).toEqual(true)
  expect(xor([], null)).toEqual(true)
  expect(xor(undefined, [])).toEqual(true)
})

Typescript test

import {xor} from 'rambda'

describe('R.xor', () => {
  it('happy', () => {
    xor(true, false) // $ExpectType boolean
  })
  it('curry', () => {
    xor(true)(false) // $ExpectType boolean
  })
})

zip

zip<K, V>(x: K[], y: V[]): KeyValuePair<K, V>[]

It will return a new array containing tuples of equally positions items from both x and y lists.

The returned list will be truncated to match the length of the shortest supplied list.

const x = [1, 2]
const y = ['A', 'B']
R.zip(x, y)
// => [[1, 'A'], [2, 'B']]

// truncates to shortest list
R.zip([...x, 3], ['A', 'B'])
// => [[1, 'A'], [2, 'B']]

Try this R.zip example in Rambda REPL

All Typescript definitions

zip<K, V>(x: K[], y: V[]): KeyValuePair<K, V>[];
zip<K>(x: K[]): <V>(y: V[]) => KeyValuePair<K, V>[];

R.zip source

export function zip(left, right) {
  if (arguments.length === 1) return _right => zip(left, _right)

  const result = []
  const length = Math.min(left.length, right.length)

  for (let i = 0; i < length; i++) {
    result[i] = [left[i], right[i]]
  }

  return result
}

Tests

import {zip} from './zip'

const array1 = [1, 2, 3]
const array2 = ['A', 'B', 'C']

test('should return an array', () => {
  const actual = zip(array1)(array2)
  expect(actual).toBeInstanceOf(Array)
})

test('should return and array or tuples', () => {
  const expected = [
    [1, 'A'],
    [2, 'B'],
    [3, 'C'],
  ]
  const actual = zip(array1, array2)
  expect(actual).toEqual(expected)
})

test('should truncate result to length of shorted input list', () => {
  const expectedA = [
    [1, 'A'],
    [2, 'B'],
  ]
  const actualA = zip([1, 2], array2)
  expect(actualA).toEqual(expectedA)

  const expectedB = [
    [1, 'A'],
    [2, 'B'],
  ]
  const actualB = zip(array1, ['A', 'B'])
  expect(actualB).toEqual(expectedB)
})

Typescript test

import {zip} from 'rambda'

describe('R.zip', () => {
  it('happy', () => {
    const array1 = [1, 2, 3]
    const array2 = ['A', 'B', 'C']

    const result = zip(array1)(array2)
    result // $ExpectType KeyValuePair<number, string>[]
  })
})

zipObj

zipObj<T, K extends string>(keys: K[], values: T[]): { [P in K]: T }

It will return a new object with keys of keys array and values of values array.

const keys = ['a', 'b', 'c']

R.zipObj(keys, [1, 2, 3])
// => {a: 1, b: 2, c: 3}

// truncates to shortest list
R.zipObj(keys, [1, 2])
// => {a: 1, b: 2}

Try this R.zipObj example in Rambda REPL

All Typescript definitions

zipObj<T, K extends string>(keys: K[], values: T[]): { [P in K]: T };
zipObj<K extends string>(keys: K[]): <T>(values: T[]) => { [P in K]: T };
zipObj<T, K extends number>(keys: K[], values: T[]): { [P in K]: T };
zipObj<K extends number>(keys: K[]): <T>(values: T[]) => { [P in K]: T };

R.zipObj source

import {take} from './take'

export function zipObj(keys, values) {
  if (arguments.length === 1) return yHolder => zipObj(keys, yHolder)

  return take(values.length, keys).reduce((prev, xInstance, i) => {
    prev[xInstance] = values[i]

    return prev
  }, {})
}

Tests

import {equals} from './equals'
import {zipObj} from './zipObj'

test('zipObj', () => {
  expect(zipObj(['a', 'b', 'c'], [1, 2, 3])).toEqual({
    a: 1,
    b: 2,
    c: 3,
  })
})

test('0', () => {
  expect(zipObj(['a', 'b'])([1, 2, 3])).toEqual({
    a: 1,
    b: 2,
  })
})

test('1', () => {
  expect(zipObj(['a', 'b', 'c'])([1, 2])).toEqual({
    a: 1,
    b: 2,
  })
})

test('ignore extra keys', () => {
  const result = zipObj(['a', 'b', 'c', 'd', 'e', 'f'], [1, 2, 3])
  const expected = {
    a: 1,
    b: 2,
    c: 3,
  }

  expect(equals(result, expected)).toBeTrue()
})

Typescript test

import {zipObj} from 'rambda'

describe('R.zipObj', () => {
  it('happy', () => {
    // this is wrong since 24.10.2020 `@types/ramda` changes
    const result = zipObj(['a', 'b', 'c', 'd'], [1, 2, 3])
    result // $ExpectType { b: number; a: number; c: number; d: number; }
  })
  it('imported from @types/ramda', () => {
    const result = zipObj(['a', 'b', 'c'], [1, 2, 3])
    const curriedResult = zipObj(['a', 'b', 'c'])([1, 2, 3])
    result // $ExpectType { b: number; a: number; c: number; }
    curriedResult // $ExpectType { b: number; a: number; c: number; }
  })
})

zipWith

zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult, list1: T[], list2: U[]): TResult[]

const list1 = [ 10, 20, 30, 40 ]
const list2 = [ 100, 200 ]

const result = R.zipWith(
  R.add, list1, list2
)
// => [110, 220]

Try this R.zipWith example in Rambda REPL

All Typescript definitions

zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult, list1: T[], list2: U[]): TResult[];
zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult, list1: T[]): (list2: U[]) => TResult[];
zipWith<T, U, TResult>(fn: (x: T, y: U) => TResult): (list1: T[], list2: U[]) => TResult[];

R.zipWith source

import {curry} from './curry'
import {take} from './take'

function zipWithFn(fn, x, y) {
  return take(x.length > y.length ? y.length : x.length, x).map(
    (xInstance, i) => fn(xInstance, y[i])
  )
}

export const zipWith = curry(zipWithFn)

Tests

import {add} from './add'
import {zipWith} from './zipWith'

const list1 = [1, 2, 3]
const list2 = [10, 20, 30, 40]
const list3 = [100, 200]

test('when second list is shorter', () => {
  const result = zipWith(add, list1, list3)
  expect(result).toEqual([101, 202])
})

test('when second list is longer', () => {
  const result = zipWith(add, list1, list2)
  expect(result).toEqual([11, 22, 33])
})

Typescript test

import {zipWith} from 'rambda'

const list1 = [1, 2]
const list2 = [10, 20, 30]

describe('R.zipWith', () => {
  it('happy', () => {
    const result = zipWith(
      (x, y) => {
        x // $ExpectType number
        y // $ExpectType number
        return `${x}-${y}`
      },
      list1,
      list2
    )

    result // $ExpectType string[]
  })
  it('curried', () => {
    const result = zipWith((x, y) => {
      x // $ExpectType unknown
      y // $ExpectType unknown
      return `${x}-${y}`
    })(list1, list2)

    result // $ExpectType string[]
  })
})

❯ CHANGELOG

WIP 7.1.0

Replace Async with Promise as return type of R.type.

7.0.2

Rambda doesn't work with pnpm due to wrong export configuration - Issue #619

7.0.1

Wrong ESM export configuration in package.json - Issue #614

7.0.0

Braking change - sync R.compose/R.pipe with @types/ramda. That is significant change so as safeguard, it will lead a major bump. Important - this lead to raising required Typescript version to 4.2.2. In other words, to use Rambda you'll need Typescript version 4.2.2 or newer.

Related commit in @types/ramda - https://github.com/DefinitelyTyped/DefinitelyTyped/commit/286eff4f76d41eb8f091e7437eabd8a60d97fc1f#diff-4f74803fa83a81e47cb17a7d8a4e46a7e451f4d9e5ce2f1bd7a70a72d91f4bc1

There are several other changes in @types/ramda as stated in this comment. This leads to change of typings for the following methods in Rambda:

-- R.unless

-- R.toString

-- R.ifElse

-- R.always

-- R.complement

-- R.cond

-- R.is

-- R.sortBy

-- R.dissoc

-- R.toPairs

-- R.assoc

-- R.toLower

-- R.toUpper

One more reason for the braking change is changing of export declarations in package.json based on this blog post and this merged Ramda's PR. This also led to renaming of babel.config.js to babel.config.cjs.
Add R.apply, R.bind and R.unapply
R.startsWith/R.endsWith now support lists as inputs. This way, it matches current Ramda behavior.
Remove unused typing for R.chain.
R.map/R.filter no longer accept bad inputs as iterable. This way, Rambda behaves more like Ramda, which also throws.
Make R.lastIndexOf follow the logic of R.indexOf.
Change R.type logic to Ramda logic. This way, R.type can return Error and Set as results.
Add missing logic in R.equals to compare sets - Issue #599
Improve list cloning - Issue #595
Handle multiple inputs with R.allPass and R.anyPass - Issue #604
Fix R.length wrong logic with inputs as {length: 123} - Issue #606.
Improve non-curry typings of R.merge by using types from mobily/ts-belt.
Improve performance of R.uniqWith.
Wrong R.update if index is -1 - PR #593
Make R.eqProps safe for falsy inputs - based on this opened Ramda PR.
Incorrect benchmarks for R.pipe/R.compose - Issue #608
Fix R.last/R.head typings - Issue #609

6.9.0

Fix slow R.uniq methods - Issue #581

Fixing R.uniq was done by improving R.indexOf which has performance implication to all methods importing R.indexOf:

R.includes
R.intersection
R.difference
R.excludes
R.symmetricDifference
R.union
R.without no longer support the following case - without('0:1', ['0', '0:1']) // => ['0']. Now it throws as the first argument should be a list, not a string. Ramda, on the other hand, returns an empty list - ramda/ramda#3086.

6.8.3

Fix Typescript build process with rambda/immutable - Issue #572
Add R.objOf method
Add R.mapObjIndexed method
Publish shorter README.md version to NPM

6.8.0

R.has use Object.prototype.hasOwnProperty- Issue #572
Expose immutable.ts typings which are Rambda typings with readonly statements - Issue #565
Fix R.intersection wrong order compared to Ramda.
R.path wrong return of null instead of undefined when path value is null - PR #577

6.7.0

Remove ts-toolbelt types from Typescript definitions. Most affected are the following methods, which lose one of its curried definitions:

R.maxBy
R.minBy
R.pathEq
R.viewOr
R.when
R.merge
R.mergeDeepRight
R.mergeLeft

6.6.0

Change R.piped typings to mimic that of R.pipe. Main difference is that R.pipe is focused on unary functions.
Fix wrong logic when R.without use R.includes while it should use array version of R.includes.
Use uglify plugin for UMD bundle.
Remove dist folder from .gitignore in order to fix Deno broken package. Issue #570
Improve R.fromPairs typings - Issue #567

6.5.3

Wrong logic where R.without use R.includes while it should use the array version of R.includes

This is Ramda bug, that Rambda also has before this release - ramda/ramda#3086

6.5.2

Wrong R.defaultTo typings - changes introduced in v6.5.0 are missing their TS equivalent.
Update dependencies

6.5.1

Fix wrong versions in changelog

6.5.0

R.defaultTo no longer accepts infinite inputs, thus it follows Ramda implementation.
R.equals supports equality of functions.
R.pipe doesn't use R.compose.
Close Issue #561 - export several internal TS interfaces and types
Close Issue #559 - improve R.propOr typings
Add CHANGELOG.md file in release files list

6.4.0

Close Issue #560 - apply immutable lint to Typescript definitions
Close Issue #553 - fix problem with curried typings of R.prop
Fix wrong R.last typing
Upgrade all rollup related dependencies
R.type supports Symbol just like Ramda.
Remove file extension in main property in package.json in order to allow experimental-modules. See also this Ramda's PR - https://github.com/ramda/ramda/pull/2678/files
Import R.indexBy/R.when/R.zipObj/R.propEq/R.complement changes from recent @types/ramda release.
R.tryCatch stop supporting asynchronous functions; the previous behaviour is exported to Rambdax as R.tryCatchAsync

6.3.1

Fix missing Evolved declaration in Typescript definition

6.3.0

Add R.takeLastWhile
Add R.dropWhile
Add R.eqProps
Add R.dropLastWhile
Add R.dropRepeats
Add R.dropRepeatsWith
Add R.evolve
Add typings for R.takeWhile when iterable is a string

6.2.0

Add R.props
Add R.zipWith
Add R.splitAt
Add R.splitWhen
Close Issue #547 - restore readonly declaration in Typescript definitions.
R.append/R.prepend now work only with arrays just like Ramda. Previous behaviour was for them to work with both arrays and strings.
Sync R.pluck typings with @types/ramda as there was a tiny difference.

6.1.0

Fix R.and wrong definition, because the function doesn't convert the result to boolean. This introduce another difference with @types/ramda.
Add R.once
Add R.or

6.0.1

Fix typing of R.reject as it wrongly declares that with object, it pass property to predicate.

6.0.0

Breaking change - R.map/R.filter/R.reject/R.forEach/R.partition doesn't pass index as second argument to the predicate, when looping over arrays. The old behaviour of map, filter and forEach can be found in Rambdax methods R.mapIndexed, R.filterIndexed and R.forEachIndexed.
Breaking change - R.all/R.none/R.any/R.find/R.findLast/R.findIndex/R.findLastIndex doesn't pass index as second argument to the predicate.
Change R.assocPath typings so the user can explicitly sets type of the new object
Typings of R.assoc match its @types/ramda counterpart.
Simplify R.forEach typings
Remove ReadonlyArray<T> pattern from Typescript definitions - not enough value for the noise it adds.

5.13.1

Fix wrong R.takeWhile

5.13.0

Add R.takeWhile method
Fix R.lensPath issue when using string as path input. The issue was introduced when fixing Issue #524 in the previous release.

5.12.1

Close Issue #524 - wrong R.assocPath when path includes numbers
R.includes throws on wrong input, i.e. R.includes(1, null)

5.12.0

Add R.move method
Add R.union method
Close Issue #519 - ts-toolbelt needs other type of export with --isolatedModules flag
Change R.when implementation and typings to match those of Ramda
R.over and R.set use R.curry instead of manual currying
R.lensPath typings support string as path, i.e. 'a.b' instead of ['a', 'b']
R.equals now supports negative zero just like Ramda.equals
R.replace uses R.curry

5.11.0

Forgot to export R.of because of wrong marker in files/index.d.ts

5.10.0

Close Issue #514 - wrong R.length with empty string

Close Issue #511 - error in ts-toolbelt library

Close Issue #510 - R.clamp should throw if min argument is greater than max argument

PR #508 - add R.of
Definition of R.curry are not same as those of @types/ramda
Definitions of R.either is same as that of R.both
Definitions of R.ifElse no longer use any type
Definition of R.flatten requires passing type for the output
Fix definition of R.propOr, R.dissoc
Fix curried definitions of R.take, R.takeLast, R.drop and R.dropLast
5.9.0
R.pickAll definition allows passing string as path to search.
R.propEq definition is now similar to that in @types/ramda.
R.none matches R.all implementation and pass index as second argument to predicate input.
R.reduce - drop support for object as iterable. Now it throws the same error as Ramda. Also instead of returning the initial value when iterable is undefined, now it throws.

Add index as additional argument to the Typescript definitions of the following methods:

R.all
R.find
R.findLast
R.findIndex
R.findLastIndex
5.8.0

Add R.mergeAll Add R.mergeDeepRight Add R.mergeLeft Add R.partition Add R.pathEq Add R.tryCatch Add R.unless Add R.whereEq Add R.where

Add R.last typing for empty array
5.7.0 Revert PR #469 as R.curry was slow | Also now R.flip throws if arity is greater than or equal to 5
5.6.3 Merge several PRs of @farwayer
PR #482 - improve R.forEach performance by not using R.map
PR #485 - improve R.map performance
PR #482 - improve R.reduce performance
Fix missing high arity typings for R.compose/pipe
R.merge definitions match those of @types/ramda
Remove dist folder from Rambda repo
5.6.2

Close Issue #476 - typesafe R.propEq definitions

Approve PR #477 - fix R.groupWith when list length is 1

5.6.1

Update ts-toolbelt files as now there is update pipeline for it.

Approve PR #474 - intruduce internal isArray helper

5.6.0

Approve PR #469 - R.flip supports any arity | implement R.curry with R.curryN add R.applySpec

5.5.0

Close Issue #464 - R.flip should handle functions with arity above 2

Close Issue #468 - fs-extra should be dev dependency as it was wrongly added as production dependency in 5.2.0

R.flip typings now match @types/ramda typings

Add R.hasPath method

Add R.mathMod typings

5.4.3

Fix R.omit typings

5.4.2

Fix R.pick typings

Close Issue #460 - R.paths should be curried

5.4.1

Close Issue #458 - wrong R.propIs typing

5.4.0

Close Issue #408 - add R.chain

5.3.0

Close Issue #430 - add R.when

Also restore R.converge, R.findLast, R.findLastIndex and R.curryN as I have forgotten to export them when releasing 5.2.0.

5.2.1

Fix Typescript comment for every method

5.2.0

Release new documentation site

Ramda repo now holds all Rambdax methods and tests

5.1.1

Add R.converge and R.curryN from PR #412

Close Issue #410 - wrong implementation of R.groupWith

Close Issue #411 - change the order of declared R.map typings rules

5.0.0

Move R.partialCurry to Rambdax(reason for major bump).

Use new type of export in Typescript definitions.

Approve PR #381 - add R.applySpec

4.6.0

Approve PR #375 - add lenses(Thank you @synthet1c)

Add R.lens

Add R.lensIndex

Add R.lensPath

Add R.lensProp

Add R.over

Add R.set

Add R.view

Sync with Ramda 0.27

Add R.paths

Add R.xor

Close Issue #373

Add R.cond

4.5.0 Add R.clamp
4.4.2 Improve R.propOr typings
4.4.1 Make R.reject has the same typing as R.filter
4.4.0 Several changes:

Close Issue #317 - add R.transpose

Close Issue #325 - R.filter should return equal values for bad inputs null and undefined

Approve suggestion for R.indexBy to accept string not only function as first argument.

Edit of R.path typings

4.2.0 Approve PR #314 - add R.and
4.1.1 Add missing typings for R.slice
4.1.0 Add R.findLast and R.findLastIndex
4.0.2 Fix R.isEmpty wrong behaviour compared to the Ramda method
4.0.1 Approve PR #289 - remove console.log in R.values method
4.0.0 Multiple breaking changes as Rambda methods are changed in order to increase the similarity between with Ramda

Add to Differences:

R.type can return 'NaN'

R.compose doesn't pass `this` context

R.clone doesn't work with number, booleans and strings as input

All breaking changes:

-- R.add works only with numbers

-- Fix R.adjust which had wrong order of arguments

-- R.adjust works when index is out of bounds

-- R.complement support function with multiple arguments

-- R.compose/pipe throws when called with no argument

-- R.clone works with Date value as input

-- R.drop/dropLast/take/takeLast always return new copy of the list/string

-- R.take/takeLast return original list/string with negative index

-- R.equals handles NaN and RegExp types

-- R.type/R.equals supports new Boolean/new Number/new Date/new String expressions

-- R.has works with non-object

-- R.ifElse pass all arguments

-- R.length works with bad input

-- R.propEq work with bad input for object argument

-- R.range work with bad inputs

-- R.times work with bad inputs

-- R.reverse works with strings

-- R.splitEvery throws on non-positive integer index

-- R.test throws just like Ramda when first argument is not regex

-- R.values works with bad inputs

-- R.zipObj ignores extra keys

3.3.0

This is pre 4.0.0 release and it contains all of the above changes

Close issue #287 - ts-toolbelt directory was changed but not reflected in files property in package.json

3.2.5

Close issue #273 - ts-toolbelt needs other type of export when isolatedModules TypeScript property

Close issue #245 - complete typings tests for methods that have more specific Typescript definitions

3.2.1 Fast fix for issue #273 - messed up typings
3.2.0 There are several changes:

Close issue #263 - broken curry typing solved by ts-toolbelt local dependency.

Add R.partialCurry typings.

Approve PR #266 that adds R.slice method.

3.1.0 This might be breaking change for Typescript users, as very different definitions are introduced. With the previous state of the definitions, it was not possible to pass dtslint typings tests.
R.either and R.both supports multiple arguments as they should.
Several methods added by @squidfunk - R.assocPath, R.symmetricDifference, R.intersperse, R.intersection and R.difference
3.0.1 Close issue #234 - wrong curry typing
3.0.0 Deprecate R.contains, while R.includes is now following Ramda API(it uses R.equals for comparision)
2.14.5 R.without needs currying
2.14.4 Close issue #227 - add index as third argument of R.reduce typings
2.14.2 Use R.curry with R.reduce as manual curry there didn't work as expected.
2.14.1 Fix wrong typescript with R.head - PR #228 pushed by @tonivj5
2.14.0 Add R.groupWith by @selfrefactor | Add R.propOr, R.mathMod, R.mean, R.median, R.negate, R.product by @ku8ar
2.13.0 Add R.identical - PR #217 pushed by @ku8ar
2.12.0 Add R.propIs - PR #213 and add R.sum - issue #207
2.11.2 Close Rambdax issue #32 - wrong R.type when function is input
2.11.1 Approve PR #182 - Changed typings to allow object as input to R.forEach and R.map
2.11.0 Approve PR #179 - R.adjust handles negative index; R.all doesn't need R.filter
2.10.2 Close issue #175 - missing typescript file
2.10.0 Approve huge and important PR #171 submitted by @helmuthdu - Add comments to each method, improve Typescript support
2.9.0 R.toPairs and R.fromPairs
2.8.0 Approve PR #165 R.clone
2.7.1 expose src | Discussed at issue #147
2.7.0 Approve PR #161 R.isEmpty
2.6.0 R.map, R.filter and R.forEach pass original object to iterator as third argument | Discussed at issue #147
2.5.0 Close issue #149 Add R.partial | R.type handles NaN
2.4.0 Major bump of Rollup; Stop building for ES5
2.3.1 Close issue #90 | Add string type of path in R.pathOr
2.3.0 Close issue #89 | Fix missing Number TS definition in R.type
2.2.0 R.defaultTo accepts indefinite number of input arguments. So the following is valid expression: const x = defaultTo('foo',null, null, 'bar')
2.1.0 Restore R.zip using WatermelonDB implementation.
2.0.0 Major version caused by removing of R.zip and R.addIndex. Issue #85 rightfully finds that the implementation of R.addIndex is not correct. This led to removing this method and also of R.zip as it had depended on it. The second change is that R.map, R.filter are passing array index as second argument when looping over arrays. The third change is that R.includes will return false if input is neigher string nor array. The previous behaviour was to throw an error. The last change is to increase the number of methods that are passing index as second argument to the predicate function.
1.2.6 Use src folder instead of modules
1.2.5 Fix omit typing
1.2.4 Add missing Typescript definitions - PR#82
1.2.2 Change curry method used across most of library methods
1.2.1 Add R.assoc | fix passing undefined to R.map and R.merge issue #77
1.2.0 Add R.min, R.minBy, R.max, R.maxBy, R.nth and R.keys
1.1.5 Close issue #74 R.zipObj
1.1.4 Close issue #71 CRA fail to build rambda
1.1.3 Approve PR #70 implement R.groupBy | Close issue #69
1.1.2 Approve PR #67 use babel-plugin-annotate-pure-calls
1.1.1 Approve PR #66 R.zip
1.1.0 R.compose accepts more than one input argument issue #65
1.0.13 Approve PR #64 R.indexOf
1.0.12 Close issue #61 make all functions modules
1.0.11 Close issue #60 problem with babelrc
1.0.10 Close issue #59 add R.dissoc
1.0.9 Close issue #58 - Incorrect R.equals
1.0.8 R.map and R.filter pass object properties when mapping over objects
1.0.7 Add R.uniqWith
1.0.6 Close issue #52 - ES5 compatible code
1.0.5 Close issue #51
1.0.4 Close issue #50 - add R.pipe typings
1.0.3 R.ifElse accept also boolean as condition argument
1.0.2 Remove typedDefaultTo and typedPathOr | Add R.pickAll and R.none
1.0.0 Major change as build is now ES6 not ES5 compatible (Related to issue #46)| Making Rambda fully tree-shakeable| Edit Typescript definition
0.9.8 Revert to ES5 compatible build - issue #46
0.9.7 Refactor for Rollup tree-shake | Remove R.padEnd and R.padStart
0.9.6 Close issue #44 - R.reverse mutates the array
0.9.5 Close issue #45 - invalid Typescript typings
0.9.4 Add R.reject and R.without (PR#41 PR#42) | Remove 'browser' field in package.json due to Webpack bug 4674
0.9.3 Add R.forEach and R.times
0.9.2 Add Typescript definitions
0.9.1 Close issue #36 - move current behaviour of defaultTo to a new method typedDefaultTo; make defaultTo follow Ramda spec; add pathOr; add typedPathOr.
0.9.0 Add R.pipe PR#35
0.8.9 Add R.isNil
0.8.8 Migrate to ES modules PR33 | Add R.flip to the API | R.map/filter works with objects
0.8.7 Change Webpack with Rollup - PR29
0.8.6 Add R.tap and R.identity
0.8.5 Add R.all, R.allPass, R.both, R.either and R.complement
0.8.4 Learning to run yarn test before yarn publish the hard way
0.8.3 Add R.always, R.T and R.F
0.8.2 Add concat, padStart, padEnd, lastIndexOf, toString, reverse, endsWith and startsWith methods
0.8.1 Add R.ifElse
0.8.0 Add R.not, R.includes | Take string as condition for R.pick and R.omit
0.7.6 Fix incorrect implementation of R.values
0.7.5 Fix incorrect implementation of R.omit
0.7.4 issue #13 - Fix R.curry, which used to return incorrectly function when called with more arguments
0.7.3 Close issue #9 - Compile to es2015; Approve PR #10 - add R.addIndex to the API
0.7.2 Add Promise support for R.type
0.7.1 Close issue #7 - add R.reduce to the API
0.7.0 Close issue #5 - change name of curry to partialCurry; add new method curry, which works just like Ramda's curry
0.6.2 Add separate documentation site via docsify

❯ Additional info

Most influential contributors

@farwayer - improving performance in R.find, R.filter; give the idea how to make benchmarks more reliable;
@thejohnfreeman - add R.assoc, R.chain;
@helmuthdu - add R.clone; help improve code style;
@jpgorman - add R.zip, R.reject, R.without, R.addIndex;
@ku8ar - add R.slice, R.propOr, R.identical, R.propIs and several math related methods; introduce the idea to display missing Ramda methods;
@romgrk - add R.groupBy, R.indexBy, R.findLast, R.findLastIndex;
@squidfunk - add R.assocPath, R.symmetricDifference, R.difference, R.intersperse;
@synthet1c - add all lenses methods; add R.applySpec, R.converge;
@vlad-zhukov - help with configuring Rollup, Babel; change export file to use ES module exports;

Rambda references

Links to Rambda

Deprecated from Used by section

SAP's Cloud SDK - This repo doesn't uses Rambda since October/2020 commit that removes Rambda

Releases

Rambda's releases before 6.4.0 were used mostly for testing purposes.

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Collection of 9 light VSCode themes

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String-fn

String utility library

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Large collection of JavaScript,Typescript and Angular related repos links

Run-fn

CLI commands for lint JS/TS files, commit git changes and upgrade of dependencies

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dizney/rambda

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