How to show row count in SSRS per grouping on variable group-by value?

Question

Essentially, I'd like to have separate row counts per grouping. I believe I'm supposed to use RowNumber. This seems to have been discussed but I'm having difficulty due to the fact that my groupby is not a string constant.

My attempts have lead to something that is similar to :

=RowNumber(Parameters!GroupBy1.Value)

The SSRS report doesn't load if I have this set as it is.

Row counts per DS work. If instead I use:

=RowNumber("NameOfMyDataSet")

I'll have row counts successfully, but without resetting per group.

How can I reset the row-count per group if I'm using a variable group-by name?

Answer 1

You need to set the scope of the function as the name of the group, not the DataSet, something like:

=RowNumber("Group1")

Edit after comment:

As above this is the name of the group created in the report, not any of the values in the DataSet.

In Designer:

Group properties: