How to use underscore's “intersection” on objects?

Question

_.intersection([], [])

only works with primitive types, right?

It doesn\'t work with objects. How can I make it work with objects (maybe b

Answer 1

I'd like to share my general solution for those cases.

I added a general function to underscore, using mixin, which performs a binary 'array' operation on two collections, according to a given Hash function:

_.mixin({
    collectionOperation: function(arr1, arr2, hash, action) {
        var iArr1 = _(arr1).indexBy(hash)
            , iArr2 = _(arr2).indexBy(hash);
        return action(_(iArr1).keys(), _(iArr2).keys()).map(function (id) {
            return iArr1[id] || iArr2[id];
        });
    }
});

Usage example:

_([{id:1,v:'q'},{id:2,v:'p'}]).collectionOperation([{id:3,v:'pq'}], 'id', _.union )

Note that 'id' may be replaced with a function.

I believe this solution is O(n+m).