Unfortunately, "Grouping" has two meanings. At first, I was thinking of "Grouping" as in a T-SQL "GROUP BY" clause. But what this really does is create a conditional stepped report, to use SSRS' terminology - or maybe it could be called a parameterized stepped report.
In this case, you're not really changing the number of rows, but reordering them with headers. This is still terrific, but I just thought I'd clarify that.
The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge. - Stephen Hawking