I'm trying to show a tablix of data where the result of a sum changes in each row. I have the rows grouped by date and sorted in descending order such that the most recent date is first. What I want to do is compare each row's sum with the sum of the previous row, e.g.
Date Sum PrevValue
---------- --- --------------
2009-09-28 3 2
2009-09-27 2 1
2009-09-26 1 5
2009-09-25 5 ...
...
I found the Previous function and thought this would be useful, but since I'm displaying my data in descending order, I get results like this:
Date Sum PrevValue
---------- --- --------------
2009-09-28 3
2009-09-27 2 3
2009-09-26 1 2
2009-09-25 5 1
...
The expression I'm using is =Previous(Sum(Fields!Sum.Value, "MyRowGroup")). I checked but there is no "Next" function to go along with Previous. How might I get the aggregate data I'm looking for while keeping my tablix sorted in descending order?