Finding the intersection of two arrays of similar objects in CoffeeScript

array-of-objects-intersection.coffee

# General pattern for intersection of two arrays of objects: 
#   collection1.filter collection2.indexOf
#
# Exercise for the reader: much optimisation can be done

myAlbums = [ 
  { id: 1, title: "The White Album" },
  { id: 2, title: "The Black Album" },
  { id: 3, title: "Hemispheres" },
  { id: 4, title: "Pure Heroine" } ]

herAlbums = [
  { id: 3, title: "Hemispheres" },
  { id: 2, title: "The Black Album" },
  { id: 5, title: "Nevermind"} ]

areAlbumsEqual = (a, b) ->
	a.id is b.id

isObjInArray = (arrayOfObj, searchObject, equalityFunction) ->
	isFoundYet = (prev, curr) -> 
		prev or equalityFunction curr, searchObject
	arrayOfObj.reduce isFoundYet, false

intersection = (collection1, collection2, equalityFunction) -> 
	collection1.filter (value) ->
		isObjInArray collection2, value, equalityFunction

console.log intersection myAlbums, herAlbums, areAlbumsEqual

This assumes some sort of ID field that can be used to determine equality, rather than doing a check on each of the objects hasOwnProperty array using a 'for own key, value of' expression, which would be needed in the absence of an ID.

I can build this, but I feel sad that I have to build this.

Oh hey! 11 days ago: jashkenas/underscore#1367