title: How to make ng-repeat filter out duplicate results
body: <p>I'm running a simple <code>ng-repeat</code> over a JSON file and want to get category names. There are about 100 objects, each belonging to a category - but there are only about 6 categories. </p>
  
  <p>My current code is this:</p>
  
  <pre><code>&lt;select ng-model="orderProp" &gt;
    &lt;option ng-repeat="place in places" value="{{place.category}}"&gt;{{place.category}}&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>The output is 100 different options, mostly duplicates. How do I use Angular to check whether a <code>{{place.category}}</code> already exists, and not create an option if it's already there?</p>
  
  <p>edit: In my javascript, <code>$scope.places = JSON data</code>, just to clarify</p>