title: Refresh aggregation results in ag-grid
body: <p>I have an <code>ag-grid</code> with rows grouped by one column and I want to show in the same line (group header) a value taken from first row in the group.</p>
  
  <p>I found out that I can use aggregation for this, but I also want to dynamically update rows and group header in accordance with this. </p>
  
  <p>To update aggregation and group header I tried to use <code>gridApi.recomputeAggregates()</code>, but this function refreshes the whole table on every call. Is it a right behavior? How can I avoid it?</p>