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 by checking the "Id" field)?

var a = [ {'id': 1, 'name': 'jake' }, {'id':4, 'name': 'jenny'} ] var b = [ {'id': 1, 'name': 'jake' }, {'id': 9, 'name': 'nick'} ] 

In this example, the result should be:

_.intersection(a, b); 

[ {'id': 1, 'name': 'jake' } ];

Answer 1

You can create another function based on underscore's function. You only have to change one line of code from the original function:

_.intersectionObjects = function(array) {     var slice = Array.prototype.slice; // added this line as a utility     var rest = slice.call(arguments, 1);     return _.filter(_.uniq(array), function(item) {       return _.every(rest, function(other) {         //return _.indexOf(other, item) >= 0;         return _.any(other, function(element) { return _.isEqual(element, item); });       });     });   }; 

In this case you'd now be using underscore's isEqual() method instead of JavaScript's equality comparer. I tried it with your example and it worked. Here is an excerpt from underscore's documentation regarding the isEqual function:

_.isEqual(object, other)  Performs an optimized deep comparison between the two objects, to determine if they should be considered equal. 

You can find the documentation here: http://documentcloud.github.com/underscore/#isEqual

I put up the code on jsFiddle so you can test and confirm it: http://jsfiddle.net/luisperezphd/jrJxT/