Hello, using R2.1.1 in Win XP I have data in the format .. ID , DateOfEntry, Drug0, DateVisit1, Drug1, DateVisit2, Drug2, DateOfDeath .. The DateOfDeath can be 999 if the patient is still alive at end of study. The number of visits can be 2, 3 or 4 per patient I want to do a time varying Cox analysis, so I need the data as: .. ID from to drug censor .. with a line for each visit. I searched the RSiteSearch but I could not find anything but I remember that somebody some time ago presented to the list a mini function that recoded the data so it could be used in this manner. If somebody in the list have a copy of that function I will appreciate if he/she send me a copy. I tried to program it but got into a knot of spaghetti code that is impossible to debug, at least by me. Thanks for any help Heberto Ghezzo Ph.D. McGill University Montreal - Canada