Is there an idiomatic way to test array equality in Coffeescript? - arrays

Question

The expression
[1, 2, 3] == [1, 2, 3]
evaluates to false in Coffeescript but is there a concise, idiomatic way to test array equality?

Answer 1

If you are dealing with arrays of numbers, and you know that there are no nulls or undefined values in your arrays, you can compare them as strings:
a = [1, 2, 3]
b = [1, 2, 3]
console.log "#{a}" is "#{b}" # true
console.log '' + a is '' + b # true
Notice, however, that this will break as soon as you start comparing arrays of other things that are not numbers:
a = [1, 2, 3]
b = ['1,2', 3]
console.log "#{a}" is "#{b}" # true
If you want a more robust solution, you can use Array#every:
arrayEqual = (a, b) ->
a.length is b.length and a.every (elem, i) -> elem is b[i]
console.log arrayEqual [1, 2, 3], [1, 2, 3] # true
console.log arrayEqual [1, 2, 3], [1, 2, '3'] # false
console.log arrayEqual [1, 2, 3], ['1,2', 3] # false
Notice that it's first comparing the lengths of the arrays so that arrayEqual [1], [1, 2, 3] doesn't return true.

Answer 2

If you don't mind introducing an Underscore.js dependency you could use some of it's utilities. It's not massively elegant, but I can't think of an easier way to do it with plain coffeescript:
a = [ 1, 2, 3 ]
b = [ 1, 2, 3 ]
equal = a.length == b.length and _.all( _.zip( a, b ), ([x,y]) -> x is y )

Answer 3

I wouldn't consider this idiomatic but this would be a way of doing it without adding an extra library:
a = [1, 2, 3, 4]
b = [22, 3, 4]
areEqual = true
maxIndex = Math.max(a.length, b.length)-1
for i in [0..maxIndex]
testEqual = a[i] is b[i]
areEqual = areEqual and testEqual
console.log areEqual
A cleaner approach would be using JavaScript's reduce() function. This is a bit shorter but I am not sure all browsers support reduce.
a = [1, 3, 4, 5]
b = [1, 3, 4, 5]
maxIndex = Math.max(a.length, b.length)-1
areEqual = true
[0..maxIndex].reduce (p, c, i, ar) -> areEqual = areEqual and (a[i] is b[i])
console.log "areEqual=#{areEqual}"

Answer 4

The following works great and requires no dependencies:
arrayEqual = (ar1, ar2) ->
JSON.stringify(ar1) is JSON.stringify(ar2)

Answer 5

I'm a big fan of Sugar.js. If you happen to be using that:
a = [1, 2, 3]
b = [1, 2, 3]
Object.equal(a, b)

Answer 6

This function returns true if arrays have same length and all values with same index have same value. It throws an error if either argument isn't an array.
isArray = Array.isArray || (subject) ->
toString.call(subject) is '[object Array]'
compareArrays = (a, b) ->
unless isArray(a) and isArray b
throw new Error '`arraysAreEqual` called with non-array'
return false if a.length isnt b.length
for valueInA, index in a
return false if b[index] isnt valueInA
true