title: ng-repeat : output only unique first letter filter
body: <p>I have an ng-repeat on a dataset that I loop using ng-repeat:</p>
  
  <pre><code>&lt;div id="songlist"&gt;
  &lt;p ng-repeat="data in output"&gt;{{data.nm}}&lt;/p&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Which outputs something like this:</p>
  
  <pre><code>&lt;div id="songlist"&gt;
  &lt;p&gt;Across The Universe&lt;/p&gt;
  &lt;p&gt;Blackbird&lt;/p&gt;
  &lt;p&gt;Baby In Black&lt;/p&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>What i'd like to do is only output the unique first letter of each song name so that it would output:</p>
  
  <pre><code>&lt;div id="songlist"&gt;
  &lt;p&gt;A&lt;/p&gt;
  &lt;p&gt;B&lt;/p&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Any ideas on how to achieve this? Thanks!</p>