Hi,
I am new to R, coming from a few years using Stata. I've been twisting my brain and checking several R and S references over the last few days to try to solve this data management problem: I have a data set with a unique patient identifier that is repeated along multiple rows, a variable with month of patient encounter, and a continous variable for cost of individual encounters. The data looks like this: ID date cost 1 "2001-01" 200.00 1 "2001-01" 123.94 1 "2001-03" 100.23 1 "2001-04" 150.34 2 "2001-03" 296.34 2 "2002-05" 156.36 I would like to obtain the median costs and boxplots for the sum of encounters happening in the first six months after the index encounter (first patient encounter) for each patient, then the mean and median costs for the costs happening from 6 to 12 months after the index encounter, and so on. Notice that the first ID has two encounters during the index date, making it more difficult to define a single row with the index encounter. Any help would be appreciated, Ricardo Ricardo Pietrobon, MD Assistant Professor of Surgery Duke University Medical Center Durham, NC 27710 US ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help