title: Angular filter works but causes "10 $digest iterations reached"
body: <p>I receive data from my back end server structured like this:</p>
  
  <pre><code>{
    name : "Mc Feast",
    owner :  "Mc Donalds"
  }, 
  {
    name : "Royale with cheese",
    owner :  "Mc Donalds"
  }, 
  {
    name : "Whopper",
    owner :  "Burger King"
  }
  </code></pre>
  
  <p>For my view I would like to "invert" the list. I.e. I want to list each owner, and for that owner list all hamburgers. I can achieve this by using the underscorejs function <code>groupBy</code> in a filter which I then use in with the <code>ng-repeat</code> directive:</p>
  
  <p>JS:</p>
  
  <pre><code>app.filter("ownerGrouping", function() {
    return function(collection) {
      return _.groupBy(collection, function(item) {
        return item.owner;
      });
    }
   });
  </code></pre>
  
  <p>HTML:</p>
  
  <pre><code>&lt;li ng-repeat="(owner, hamburgerList) in hamburgers | ownerGrouping"&gt;
    {{owner}}:  
    &lt;ul&gt;
      &lt;li ng-repeat="burger in hamburgerList | orderBy : 'name'"&gt;{{burger.name}}&lt;/li&gt;
    &lt;/ul&gt;
  &lt;/li&gt;
  </code></pre>
  
  <p>This works as expected but I get an enormous error stack trace when the list is rendered with the error message "10 $digest iterations reached". I have a hard time seeing how my code creates an infinite loop which is implied by this message. Does any one know why?</p>
  
  <p>Here is a link to a plunk with the code: <a href="http://plnkr.co/edit/8kbVuWhOMlMojp0E5Qbs?p=preview">http://plnkr.co/edit/8kbVuWhOMlMojp0E5Qbs?p=preview</a></p>