Change the grouping of the fields on the fly
I have a sales report on tabular. Group by Shop name and a second group of products. This way user can see info about sales in each shop by products.
Now user wants to see sales by product in all shops together. To do so he must edit datapage and change the fields order so the products will be on top.
The idea is to allow users to change fields order on result set. This way they can change the groupings without editing the datapage
Just create two reports and put a button on each page to switch to the other format.