dotnet · BillWagner · Feb 28, 2022 · Feb 27, 2022
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+module Enumerable1
+
+// <Snippet6>
+open System
+open System.Linq
+
+let data = [| 1; 2; 3; 4 |]
+let average = 
+   data.Where(fun num -> num > 4).Average();
+printfn $"The average of numbers greater than 4 is {average}"
+// The example displays the following output:
+//    Unhandled Exception: System.InvalidOperationException: Sequence contains no elements
+//       at System.Linq.Enumerable.Average(IEnumerable`1 source)
+//       at <StartupCode$fs>.main()
+// </Snippet6>
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+module Enumerable2
+
+// <Snippet7>
+open System
+open System.Linq
+
+let dbQueryResults = [| 1; 2; 3; 4 |]
+let moreThan4 = 
+    dbQueryResults.Where(fun num -> num > 4)
+
+if moreThan4.Any() then
+    printfn $"Average value of numbers greater than 4: {moreThan4.Average()}:"
+else
+    // handle empty collection
+    printfn "The dataset has no values greater than 4."
+
+// The example displays the following output:
+//       The dataset has no values greater than 4.
+// </Snippet7>
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+module Enumerable3
+
+// <Snippet8>
+open System
+open System.Linq
+
+let dbQueryResults = [| 1; 2; 3; 4 |]
+
+let firstNum = dbQueryResults.First(fun n -> n > 4)
+
+printfn $"The first value greater than 4 is {firstNum}"
+
+// The example displays the following output:
+//    Unhandled Exception: System.InvalidOperationException:
+//       Sequence contains no matching element
+//       at System.Linq.Enumerable.First[TSource](IEnumerable`1 source, Func`2 predicate)
+//       at <StartupCode$fs>.main()
+// </Snippet8>
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+module Enumerable4
+
+// <Snippet9>
+open System
+open System.Linq
+
+let dbQueryResults = [| 1; 2; 3; 4 |]
+
+let firstNum = dbQueryResults.FirstOrDefault(fun n -> n > 4)
+
+if firstNum = 0 then
+    printfn "No value is greater than 4."
+else
+    printfn $"The first value greater than 4 is {firstNum}"
+
+// The example displays the following output:
+//       No value is greater than 4.
+// </Snippet9>
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+module Enumerable5
+
+// <Snippet10>
+open System
+open System.Linq
+
+let dbQueryResults = [| 1; 2; 3; 4 |]
+
+let singleObject = dbQueryResults.Single(fun value -> value > 4)
+
+// Display results.
+printfn $"{singleObject} is the only value greater than 4"
+
+// The example displays the following output:
+//    Unhandled Exception: System.InvalidOperationException:
+//       Sequence contains no matching element
+//       at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source, Func`2 predicate)
+//       at <StartupCode$fs>.main()
+// </Snippet10>
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+module Enumerable6
+
+// <Snippet11>
+open System
+open System.Linq
+
+let dbQueryResults = [| 1; 2; 3; 4 |]
+
+let singleObject = dbQueryResults.SingleOrDefault(fun value -> value > 2)
+
+if singleObject <> 0 then
+    printfn $"{singleObject} is the only value greater than 2"
+else
+    // Handle an empty collection.
+    printfn "No value is greater than 2"
+
+// The example displays the following output:
+//    Unhandled Exception: System.InvalidOperationException:
+//       Sequence contains more than one matching element
+//       at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)
+//       at <StartupCode$fs>.main()
+// </Snippet11>
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+module Iterating1
+
+// <Snippet1>
+open System
+
+let numbers = ResizeArray [| 1; 2; 3; 4; 5 |]
+for number in numbers do
+    let square = Math.Pow(number, 2) |> int
+    printfn $"{number}^{square}"
+    printfn $"Adding {square} to the collection...\n"
+    numbers.Add square
+
+// The example displays the following output:
+//    1^1
+//    Adding 1 to the collection...
+//
+//
+//    Unhandled Exception: System.InvalidOperationException: Collection was modified
+//       enumeration operation may not execute.
+//       at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
+//       at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
+//       at <StartupCode$fs>.main()
+// </Snippet1>
@@ -0,0 +1,37 @@
+module Iterating2
+
+// <Snippet2>
+open System
+open System.Collections.Generic
+
+let numbers = ResizeArray [| 1; 2; 3; 4; 5 |]
+
+let upperBound = numbers.Count - 1
+for i = 0 to upperBound do
+    let square = Math.Pow(numbers[i], 2) |> int
+    printfn $"{numbers[i]}^{square}"
+    printfn $"Adding {square} to the collection...\n"
+    numbers.Add square
+
+printfn "Elements now in the collection: "
+for number in numbers do
+    printf $"{number}    "
+// The example displays the following output:
+//    1^1
+//    Adding 1 to the collection...
+//
+//    2^4
+//    Adding 4 to the collection...
+//
+//    3^9
+//    Adding 9 to the collection...
+//
+//    4^16
+//    Adding 16 to the collection...
+//
+//    5^25
+//    Adding 25 to the collection...
+//
+//    Elements now in the collection:
+//    1    2    3    4    5    1    4    9    16    25
+// </Snippet2>
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+module Iterating3
+
+// <Snippet3>
+open System
+open System.Collections.Generic
+
+let numbers = ResizeArray [| 1; 2; 3; 4; 5 |]
+let temp = ResizeArray()
+
+// Square each number and store it in a temporary collection.
+for number in numbers do
+    let square = Math.Pow(number, 2) |> int
+    temp.Add square
+
+// Combine the numbers into a single array.
+let combined = Array.zeroCreate<int> (numbers.Count + temp.Count)
+Array.Copy(numbers.ToArray(), 0, combined, 0, numbers.Count)
+Array.Copy(temp.ToArray(), 0, combined, numbers.Count, temp.Count)
+
+// Iterate the array.
+for value in combined do
+    printf $"{value}    "
+// The example displays the following output:
+//       1    2    3    4    5    1    4    9    16    25
+// </Snippet3>
@@ -0,0 +1,27 @@
+module List_Sort1
+
+// <Snippet12>
+type Person(firstName: string, lastName: string) =
+    member val FirstName = firstName with get, set
+    member val LastName = lastName with get, set
+
+let people = ResizeArray()
+
+people.Add(Person("John", "Doe"))
+people.Add(Person("Jane", "Doe"))
+people.Sort()
+for person in people do
+    printfn $"{person.FirstName} {person.LastName}"
+// The example displays the following output:
+//    Unhandled Exception: System.InvalidOperationException: Failed to compare two elements in the array. --->
+//       System.ArgumentException: At least one object must implement IComparable.
+//       at System.Collections.Comparer.Compare(Object a, Object b)
+//       at System.Collections.Generic.ArraySortHelper`1.SwapIfGreater(T[] keys, IComparer`1 comparer, Int32 a, Int32 b)
+//       at System.Collections.Generic.ArraySortHelper`1.DepthLimitedQuickSort(T[] keys, Int32 left, Int32 right, IComparer`1 comparer, Int32 depthLimit)
+//       at System.Collections.Generic.ArraySortHelper`1.Sort(T[] keys, Int32 index, Int32 length, IComparer`1 comparer)
+//       --- End of inner exception stack trace ---
+//       at System.Collections.Generic.ArraySortHelper`1.Sort(T[] keys, Int32 index, Int32 length, IComparer`1 comparer)
+//       at System.Array.Sort[T](T[] array, Int32 index, Int32 length, IComparer`1 comparer)
+//       at System.Collections.Generic.List`1.Sort(Int32 index, Int32 count, IComparer`1 comparer)
+//       at <StartupCode$fs>.main()
+// </Snippet12>
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+module List_Sort2
+
+// <Snippet13>
+open System
+
+type Person(firstName: string, lastName: string) =
+    member val FirstName = firstName with get, set
+    member val LastName = lastName with get, set
+
+    interface IComparable<Person> with
+        member this.CompareTo(other) =
+            compare $"{this.LastName} {this.FirstName}" $"{other.LastName} {other.FirstName}"
+
+let people = ResizeArray()
+
+people.Add(new Person("John", "Doe"))
+people.Add(new Person("Jane", "Doe"))
+people.Sort()
+for person in people do
+    printfn $"{person.FirstName} {person.LastName}"
+// The example displays the following output:
+//       Jane Doe
+//       John Doe
+// </Snippet13>
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+module List_Sort3
+
+// <Snippet14>
+open System
+open System.Collections.Generic
+
+type Person(firstName, lastName) =
+    member val FirstName = firstName with get, set
+    member val LastName = lastName with get, set
+
+type PersonComparer() =
+    interface IComparer<Person> with
+        member _.Compare(x: Person, y: Person) =
+            $"{x.LastName} {x.FirstName}".CompareTo $"{y.LastName} {y.FirstName}"
+
+let people = ResizeArray()
+
+people.Add(Person("John", "Doe"))
+people.Add(Person("Jane", "Doe"))
+people.Sort(PersonComparer())
+for person in people do
+    printfn $"{person.FirstName} {person.LastName}"
+// The example displays the following output:
+//       Jane Doe
+//       John Doe
+// </Snippet14>
@@ -0,0 +1,25 @@
+module List_Sort4
+
+// <Snippet15>
+open System
+open System.Collections.Generic
+
+type Person(firstName, lastName) =
+    member val FirstName = firstName with get, set
+    member val LastName = lastName with get, set
+
+let personComparison (x: Person) (y: Person) =
+    $"{x.LastName} {x.FirstName}".CompareTo $"{y.LastName} {y.FirstName}"
+
+let people = ResizeArray()
+
+people.Add(Person("John", "Doe"))
+people.Add(Person("Jane", "Doe"))
+people.Sort personComparison
+for person in people do
+    printfn $"{person.FirstName} {person.LastName}"
+
+// The example displays the following output:
+//       Jane Doe
+//       John Doe
+// </Snippet15>
@@ -0,0 +1,21 @@
+module Nullable1
+
+// <Snippet4>
+open System
+open System.Linq
+
+let queryResult = [| Nullable 1; Nullable 2; Nullable(); Nullable 4 |]
+let map = queryResult.Select(fun nullableInt -> nullableInt.Value)
+
+// Display list.
+for num in map do
+    printf $"{num} "
+printfn ""
+// The example displays the following output:
+//    1 2
+//    Unhandled Exception: System.InvalidOperationException: Nullable object must have a value.
+//       at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
+//       at Example.<Main>b__0(Nullable`1 nullableInt)
+//       at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
+//       at <StartupCode$fs>.main()
+// </Snippet4>
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+module Nullable2
+
+// <Snippet5>
+open System
+open System.Linq
+
+let queryResult = [| Nullable 1; Nullable 2; Nullable(); Nullable 4 |]
+let numbers = queryResult.Select(fun nullableInt -> nullableInt.GetValueOrDefault())
+
+// Display list using Nullable<int>.HasValue.
+for number in numbers do
+    printf $"{number} "
+printfn ""
+
+let numbers2 = queryResult.Select(fun nullableInt -> if nullableInt.HasValue then nullableInt.Value else -1)
+// Display list using Nullable<int>.GetValueOrDefault.
+for number in numbers2 do
+    printf $"{number} "
+printfn ""
+// The example displays the following output:
+//       1 2 0 4
+//       1 2 -1 4
+// </Snippet5>
@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="Iterating1.fs" />
+    <Compile Include="Iterating2.fs" />
+    <Compile Include="Iterating3.fs" />
+    <Compile Include="List_Sort1.fs" />
+    <Compile Include="List_Sort2.fs" />
+    <Compile Include="List_Sort3.fs" />
+    <Compile Include="List_Sort4.fs" />
+    <Compile Include="Nullable1.fs" />
+    <Compile Include="Nullable2.fs" />
+    <Compile Include="Enumerable1.fs" />
+    <Compile Include="Enumerable2.fs" />
+    <Compile Include="Enumerable3.fs" />
+    <Compile Include="Enumerable4.fs" />
+    <Compile Include="Enumerable5.fs" />
+    <Compile Include="Enumerable6.fs" />
+  </ItemGroup>
+</Project>