Hi Reeza, Thanks for your inputs. I expect that the output will have all the variables given in the sample and will create two new variables 'startdate' and 'enddate'. Startdate represents when the first prescription was filled(is equal to filldate). Enddate is when the prescription was stopped(is equal to filldatethru). So, I need to keep start and end dates for each unique patient who was prescribed a drug (whose rx_flag=1). However, when I try running the code which I have mentioned, it gives me missing values for startdate even for rx_flag=1. So, I am not sure how I should be specifying that condition. Should it be if rx_flag=1 then startdate=filldate? I will look into the RETAIN statement that you mentioned. Thanks again!
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