The title might be a bit misleading but I hope you can help me.
I have some data (let's say a Web Log file) and I want to be able to compare
multiple items with each other. For example I want to know what items are
popular in certain user groups, which means that I want to find items which
got many successive hits from users from that group in a short period of
Until now I only worked on the rows in an isolated manner, that is items
could be filtered or modified, without any knowledge of other records, but
this now requires to consider multiple records, and I have no clue as to how
approach this problem.