Underscore Unwind like MongoDB operation

unwind.js

_.mixin({
	unwind: function(arr, field) {
		return _.flatten(_.map(arr, function(o) {
				return _.map(o[field], function(val) {
					var cloned = _.clone(o);
					cloned[field] = val;
					return cloned;
				});
		}));
	}
})