have a look at ave() and/or tapply(). I hope it helps.
Best, Dimitris Reynaerts, Jo wrote:
Dear R users I have a data frame that looks like this: m j X1 X2 1 1 1 2 1 ... 1 J 2 1 2 2 2 ... 2 J . . . M 1 M 2 M ... M J The data frame essentially looks like a panel: m and j are indicators where m is 1:M and j is 1:J (and M > J); X1 and X2 are variables. I would like to construct and add new variables to the data frame that are m- and j- specific, e.g., compute X3 where X3 is the sum of X1 of all j in m, and this for each m. The new variable X3 is then added to the data frame (and is the same for all rows with the same m indicator). How can I program this efficiently without running loops? Thanks in advance Jo Reynaerts Ph.D. student LICOS Centre for Institutions and Economic Performance Katholieke Universiteit Leuven Debériotstraat 34/3511 B-3000 Leuven Belgium jo.reynae...@econ.kuleuven.be<mailto:jo.reynae...@econ.kuleuven.be> [[alternative HTML version deleted]] ------------------------------------------------------------------------ ______________________________________________ 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.
-- Dimitris Rizopoulos Assistant Professor Department of Biostatistics Erasmus University Medical Center Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands Tel: +31/(0)10/7043478 Fax: +31/(0)10/7043014 ______________________________________________ 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.
