title: ng-grid sum of values in aggregate row
body: <p>I have an ng-grid with three columns (name, value, machine) that displays metrics (name, value) from three different computers (as indicated in machine column). Rather than displaying three lines for each metric, I have set <code>groups: ['name']</code> in the gridOptions; however, I cannot figure out how to make the aggregate row display the sum of the values. Is there a way to access the values of the rows in each group to calculate a sum?</p>
  
  <p>This is what I want to see (7, 10, 4, 6 on the aggregate rows in the value column):</p>
  
  <pre><code>  NAME           VALUE     MACHINE
  v metric1 (3)    7
    metric1        3         comp-a
    metric1        2         comp-b
    metric1        2         comp-c
  &gt; metric2 (3)    10
  &gt; metric3 (3)    4
  v metric4 (3)    6
    metric4        5         comp-a
    metric4        0         comp-b
    metric5        1         comp-c
  </code></pre>
  
  <p>Thanks for your help!</p>