title: calling a custom function for groupHeaderTpl- extJS
body: <p>I am using a custom function which I am calling under a column like this to change the format. I have defined the function which works well.</p>
  
  <pre><code>renderer: function(v, params, record,row){
              return readableDuration(v) + ' Hrs';
          }
  </code></pre>
  
  <p>Now I want to use the same under <code>groupHeaderTpl</code> by passing an argument. But I am not able to get it. Could you help? Here is my code for <code>groupHeaderTpl</code></p>
  
  <pre><code>groupHeaderTpl:[
                      '{name} {[readableDuration({[values.rows[0].data.tbp]})]}'
  
             ]
  </code></pre>
  
  <p>where <code>tbp</code> is a parameter I read from respective json data</p>
  
  <p>Thanks in advance</p>