How do I number rows in a DataWindow when I have groups defined?

Suppose you want to display a row number for each row in a DW. Easy enough – just make a computed column with the value GetRow().

Now suppose you have a group in the DW, and want the row number to start over for every group break. To do this, just create a computed column with the value GetRow() – First(GetRow() for Group 1) + 1.