Hello,
Since there is no good way to search for a specific field in aggregates I would suggest an easy way to make the group by. Something, similar to what we have with the sort functionality, where you can select a field from the result set.
My suggestion would be to create a new tab on the aggregate header so that we can introduce the group by that we want. Possible a multiple select would also be nice.
Attached I am adding rough scratch.
