I'm in a similar situation though in SSRS 2008.
I am interested in knowing how to write an expression that says;
iif the row_description is A then return Count(item_id)
Iif the row_description is B then return AVG(price)
iif the row_description is C then return Count of C's item_ids /iif row_description is A then Count of A's item_ids.
In other words, I need a top count to be based on a different condition than the bottom count.
what approach and functions to pursue?