title: ExtJS 4 - Grid Store 'sum' function always returning NaN
body: <p>I have a grid in which I need to perform 'sum' &amp; 'average' operations on columns and display these values in an alert box.</p>
  
  <p>I am trying to use the 'sum' and 'average' functions of store but always the value returned in NaN.</p>
  
  <pre><code>storeCpEirDistByVoaGrid.sum('allocatedBr');
  </code></pre>
  
  <p>I have specified the 'type' as 'int' for these column in model but no luck. Also, I am calculating these values once the grid has been rendered and values are populated, but still value returned is NaN.</p>
  
  <p>Could anyone please guide that what could be going wrong?</p>
  
  <p>Thanks in advance.</p>