title: Retrieve list of a specific attribute from a Backbone collection
body: <p>I'm looking for a way to, from a backbone collection, retrieve some kind of array of one specific attribute. </p>
  
  <pre><code>var SomeModel = Backbone.Model.extend({
      defaults: function() {
          return {
              attr1: "something",
              attr2: "something",
              attr3: "darkside"
          };
      }
  });
  
  var SomeCollection = Backbone.Collection.extend({
      model: SomeModel,
      url: '/data.json',
  });
  </code></pre>
  
  <p>Now assume I have something like above and I only want a collection/array/similar with only the attribute 'attr3'. Is there any nice way to get this (not by manually iterating through the SomeCollection and building a new Collection)? My understanding from underscore function "filter" is that it returns the entire SomeModel based on a certain premise, i.e. this is not what I want. Ideas?</p>
  
  <p>Thanks </p>