title: p:datatable summary row calculation
body: <p>I have a <code>p:dataTable</code> pretty similar to the <a href="http://www.primefaces.org/showcase/ui/data/datatable/summaryRow.xhtml" rel="nofollow">showcase</a>.
  Unfortunatly, the showcase uses randomly generated values for the <code>p:summaryRow</code>.</p>
  
  <p>Refering to the showcase, imagine the car had a price attribute.</p>
  
  <p><strong>How would I sum up the price for the cars grouped by the specified column for displaying it in the summary row?</strong></p>