Did you find a way to do this Ali?
Dilyan I don't think your examples are helpful in this case. Everything you linked to operates on the assumption that a single row will produce a SINGLE grouping key. In this case, each row may belong to multiple groups. See my attached example screen shot. If we were to group by "Employee Roles", the group "Coder" should have employee IDs 2 and 3, and the group "Pleb" would have employee IDs 2 (again) and 1 etc.
I suspect internally something like this is happening when using the generic group descriptor:
which means it's not possible to have a single row entity appearing in more than 1 group.
Any advice would be appreciated.