?aggregate aggregate(X~ID, your.data.frame.goes.here, "mean")
Mikhail > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf Of Julia Moeller > Sent: Friday, August 12, 2011 10:10 AM > To: r-help@r-project.org > Subject: [R] recode Variable in dependence of values of two other variables > > Hi, > > as an R-beginner, I have a recoding problem and hope you can help me: > > I am working on a SPSS dataset, which I loaded into R (load("C:/...) > > I have 2 existing Variables: "ID" and "X" , and one variable to be > computed: meanX.dependID (=mean of X for all rows in which ID has the same > value) > > ID = subject ID. Since it is a longitudinal dataset, there are repeated > measurement points for each subject, each of which appears in a new row. > So, each ID value appears in many rows. (e.g. ID ==1 in row 1:5; ID ==2 in > rows 6:8 etc). > > > Now: For all rows, in which ID has a certain value, meanX.dependID shall be > the mean of X in for these rows. How can I automatisize that, without > having to specify the number of the rows each time? > > e.g. > > > ID X meanX.dependID > 1 2 2.25 > 1 3 2.25 > 1 1 2.25 > 1 3 2.25 > 2 5 3.3 > 2 2 3.3 > 2 3 3.3 > 3 4 3 > 3 1 3 > 3 2 3 > 3 3 3 > 3 4 3 > 3 5 3 > > > Thanks a lot! Hope this is the right place to post, if not, please tell me! > best, > Julia ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.