title: AngularJS: HTML select to use values from map
body: <p>Have this HTML:</p>
  
  <pre><code>&lt;select ng-model="group" ng-options="g.key for g in groups"&gt;&lt;/select&gt;
  </code></pre>
  
  <p>Although <code>$scope.groups</code> is map <code>{'a':'', 'b':'', 'c':''}</code>
  I'd like select to display map keys: a,b,c</p>
  
  <p>Currently it selects nothing.
  How to change <code>ng-options</code>?\</p>
  
  <p><strong>UPDATE 1</strong></p>
  
  <p><code>g for g in Object.keys(groups)</code> does not work either.</p>