title: key-value pairs in ng-options
body: <p>I need to use an <em>associative array</em> as data source for my <code>select</code> options using AngularJS.</p>
  
  <p>Is it possible to use an array like this?</p>
  
  <pre><code>{
      "key1": "val1",
      "key2": "val2",
      "key3": "val3",
      ...
  }
  </code></pre>
  
  <p>and get something like this:</p>
  
  <pre><code>&lt;select&gt;
      &lt;option value="key1"&gt;val1&lt;/option&gt;
      &lt;option value="key2"&gt;val2&lt;/option&gt;
      &lt;option value="key3"&gt;val3&lt;/option&gt;
      ...
  &lt;/select&gt;
  </code></pre>
  
  <p>I read <a href="http://docs.angularjs.org/api/ng.directive:select" rel="noreferrer">docs</a>, but I can't understand how to achieve this.</p>