%VID Question

I'm Trying to create a "Windowing Function" In Cache similar to SQL Server. I'm trying to create a Row Number for every account number (Example Below). I know I can use the %Vid function to create the Row Number but I need the row number to reset with every new account number. In SQL Server it would be Row_Number over (Partition by account number order by account number). and Example of what I am trying to create is below.

Row Number          Account Number

1                                             1

2                                             1

3                                             1

1                                             2

2                                             2

1                                             3

1                                             4