A Meteor package making it easy to reactively calculate sums in Mongo collections on the client.

This package adds a property called sum to Mongo.Cursor.prototype on the client. It can be used to reactively calculate sums in a collection. Example:

HighScores = new Mogno.Collection()
HighScores.insert({score:   10})
HighScores.insert({score:  100})
HighScores.insert({score: 1000})

Tracker.autorun(function(){
	console.log("The sum of all scores is "+HighScores.find({}).sum('score'))
})

// The follwing has been printed to the console: The sum of all scores is 1110

HighScores.insert({score: 1})

// The follwing has been printed to the console: The sum of all scores is 1111

cursor.sum(fieldOrFunc)

If the parameter fieldOrFunc is a string, it will return the sum of all the values doc[fieldOrString] in the cursor.

If the parameter fieldOrFunc is a function, it will return the sum of all the values fieldOrFunc(doc) in the cursor.

Note that cursor.sum is affected by tranformations, and that it overall will work the same way as cursor.count (regarding reactivity).