Previous Function

Hello,

I have a table in XIr 2 with the following columns

1. Group

2. Open Date

3. Id

I have put a break on Group and i want to use Previous function to get the previous open date within that group. But no matter what context i try i get the Previous open date in the first row for the preivious group

Eg

Group Open Date Id Previous

A1 12/12/2008 101

A1 12/13/2008 102 12/12/2008

A1 12/14/2008 103 12/13/2008

A2 12/15/2008 104 12/14/2008

A2 12/16/2008 105 12/15/2008

If you see the 4 the row, i want that to be blank but instead i get the pervious row's (groups) date --12/14/2008.

Is there any way to handle this? Any help is much appreciated

Thanks,

Anand