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2010 Jun 26
2
Recoding dates to session id in a longitudinal dataset
Hi, I'm fairly new to R but I have a large dataset (300000 obs) containing patient material. Some patients came 2-9 times during the three year observation period. The patients are identified by a unique idnr, the sessions can be distinguished using the session date. How can I recode the date of the session to a session id (1-9). This would be necessary to obtain information and do some