Hi All; I have a situations which seems easy to accomplish, yet after many attempts am still unsuccessful. I have one dataset of events with these variables: id (identifier for a subject), id_after (id for the row following), time_diff (time between the current row and the row after),  and duration (the time the subject spent for the current row). Current: ID ID_After time_diff Duration 1 1 1 0 1 1 1 1 1 1 18 1 1 2 20 2 2 2 1 1 What I would like to do is create a new variable called 'session', which will mark each row as being part of a particular session with some specified logic I put in place. Thus this new column would act like a session ID to which I can then do calculation like 'how many sessions does a user have?' or 'how long is the average session?' The resulting table would look like this where there are 3 unique sessions: ID ID_After time_diff Duration Session 1 1 1 0 1 1 1 1 1 1 1 1 18 1 1 1 2 20 2 2 2 2 1 1 3 Here's my logic: First declare a variable sessionID and set it to 1 and then in the do-loop do this: session=&sessionID.; if id = id_after and time_diff <2 or id = id_after and time_dif <= duration then %let sessionID=%eval(&sessionID.); else %let sessionID=%eval(&sessionID.+1); Any ideas how I can get to the final goal of this loop with this logic? I have looked at SQL cursors and some iterative Macros with do loops but all to no avail. Any help is greatly appreciative. Thanks, T ... View more