Group by and count

[J Do]

How can I count how many records per group by item.
ex:
group by Category         count Subcategory           
------------------------------------------------------------------
Category1                              2 (sub1,sub2)                                            
Category2                              3 (sub3,sub4,sub5)          

                                                   
Thanks

[J Do]

I got a solution

First, I row group with Category, then on the same row detail, I have an expression =Count(Fields.SubCategory)