title: Operations in sortableAttributes (CListView)
body: <p>I want to give some operation in sortableAttributes like difference between vote_up and vote_down.</p>
  
  <p>Is it possible?</p>
  
  <pre><code>'sortableAttributes'=&gt;array(
              'id','created','vote_up-vote_down'=&gt;'Votes',
  ),
  </code></pre>