creating different groupings depending on parameter

hi,

I have a parameter that lets users choose which field to sort the report on.

I added a row group, adding the fields that I want to appear inside the group.  I see my fields in the 'Row Groups' description at the bottom of my report in design mode.

I added this code to the function of the first field in that row group:  ( "= IIF( Parameters!GroupedBy.Value = "location",Fields!Location.Value, Fields!.Date.value")...

Is that possible what I'm trying?  Or, do I have to create two groupings for the row and apply one or the other depending on what the user selected for grouping?

I have found examples here and there, but they don't do exactly the same thing.  I wanted to know if this was possible what I'm trying to do - before wasting too much of my time.

Thanks