Backbone.js Underscore.js filtering a collection v

Question

I'm basically trying to do what is done with this question, but with an array and return all objects using the values of the corresponding array, not just the value: Filter backbone collection by attribute value

My natural instinct is to use _.filter or _.partition on the persons collection, but am confused on how these are being compared & returned and am not getting the desired outcome.

With the following, passing the id in via the router:

friendsRoute: function(id){                                                                       
  persons = new App.Collections.Persons();                                                   
  persons.fetch().done(function(){                                                           
    var single = persons.find(function(i){                                                   
      return i.get('id') == id;                                                              
    });                                                                                      
    var friendsIds = single.get('friends');


    var friends = ?


    //var friendsList = new App.Views.FriendsList();
    //friendsList.render({ friends: friends });
  });                                                                                        
},                                                                                           

I have a friendsIds array (Joe's friends):

friendsIds = [1,4,5]

And trying to get the matched ids from the following JSON and display their names in my friendsList view:

[
  { "id": 1, "name": "Steve", "age": 22, "friends": [4] },
  { "id": 2, "name": "Mary", "age": 18, "friends": [1,3] },
  { "id": 3, "name": "Joe", "age": 43, "friends": [1,4,5] },
  { "id": 4, "name": "Tommy", "age": 19, "friends": [1] },
  { "id": 5, "name": "Leslie", "age": 27, "friends": [2,4] }
]

Answer 1

var friendsIds = [1,4,5];
var friends = [
  { "id": 1, "name": "Steve", "age": 22, "friends": [4] },
  { "id": 2, "name": "Mary", "age": 18, "friends": [1,3] },
  { "id": 3, "name": "Joe", "age": 43, "friends": [1,4,5] },
  { "id": 4, "name": "Tommy", "age": 19, "friends": [1] },
  { "id": 5, "name": "Leslie", "age": 27, "friends": [2,4] }
];
var filteredFriends = _.filter(friends, function(frnd){
return _.contains(friendsIds, frnd.id);
});
console.log(filteredFriends);

See the difference in performance with filter and map here

Make use of filter and contains

FIDDLE

Answer 2

I think you could use a combination of map and findWhere to do this:

var friends = _.map(friendsIds, function(id) { 
    return _.findWhere(persons, { 'id': id }); 
});