I've been searching for hours to figure out how to do this. Essentially what I want to do is group data based on one column, create a summary for that grouping, then sort the groups based on the summary.
Using one of their kitchen sink examples, I would like to be able to sort these groups by summary value rate.
http://examples.sencha.com/extjs/6.0.0/examples/classic/grid/group-summary-grid.html
This can be done using a grouper with a sorterFn. The sorterFn should compare the summary values you are sorting by. For the kitchen sink example you mentioned, if you want to sort by the sum of the estimate column while grouping by the project column, the grouper would look like:
The grouper can be applied using:
See fiddle: https://fiddle.sencha.com/#fiddle/1im3