title: Get length of object by nested object id?
body: <p>I'm currently using underscore to the length of an object using <code>_.size(obj)</code> and that is fine but I'm wondering how I could go a little deeper and get the length of objects who's id's equal <code>123</code> in my example. I'm not sure if this is something that can be achieved by using underscore or do I need to use a for..in loop and make some kind of count?</p>
  
  <p><strong>JS</strong>
  console.clear();</p>
  
  <pre><code>var obj = {
      'ABC': {
          id: '123',
          name: 'Sesame Street'
      }, 
      'DEF': {
          id: '123',
          name: 'Sesame Street'
      }, 
      'GHI': {
          id: '456',
          name: 'Nowhere Street'
      }
  };
  
  console.log('Get length of obj', _.size(obj));
  console.log('Get length of obj with id == 123??');
  </code></pre>
  
  <p><strong>JSFiddle:</strong> <a href="http://jsfiddle.net/kyllle/0yam33ow/" rel="nofollow">http://jsfiddle.net/kyllle/0yam33ow/</a></p>