Filter for the Max of a Running Count

[stanleytheyak]

I have a running count that looks like this: running-count ([Comments] for [Message ID], [Contact ID])  What I would like to do is create a filter that returns ONLY the highest number in that running-count.  I'm fairly new to Cognos and have not been able to find a simple version of this in any of the forums.  Any help is appreciated.