Merging two collections using Underscore.JS

Question

Provided I have two collections:

c1 - [{a:1},{a:2},{a:3}]

and

c2 - [{a:1},{a:7},{a:8}]

what's the fastest way to add unique items from c2 into c1 using Underscore.JS? The real numbers in collections would be 2K for c1 and 500 for c2, the operation is performed often, so must be performant!

Update 1 - I'm only using Underscore.JS for a few days, I couldn't find a way to add one collection into another (I can filter c2 myself) - is that trivial in Underscore.JS?

Answer 1

The following will:

• create a new array that contains all the elements of c1 and c2. See union.
• from that mix, create a new array that contains only the unique elements. See uniq.

Note that this would work only if all your objects have the property a.

_.uniq(_.union(c1, c2), false, function(item, key, a){ return item.a; }); 

You can find other options in this question.