adapted from the help files of rowsum x <- matrix(runif(100), ncol=5) group <- sample(1:8, 20, TRUE) xsum <- rowsum(x, group) sweep(xsum, 1, table(group), "/")
or aggregate(x, list(group), mean)[-1] b 2010/1/15 Joel Fürstenberg-Hägg <joel_furstenberg_h...@hotmail.com>: > > Hi all, > > > > I want to calculate the row wise mean of groups of columns in a matrix M. All > columns belonging to the same group have the same column name. My idea is to > create a new vector V containing these column names, but after first removing > the duplicates. Then I would calculate the means using for instance rowMean() > and by comparing the column names of M with the vector V, getting the indices > of the columns to use. > > > > What do you think, is it a good idea or not? If yes, any suggestions how to > do it? If no, is there any alternative solution that might work better? > > > > > > > > All the best, > > > > Joel > > _________________________________________________________________ > Lagra alla dina foton på Skydrive. Det är enkelt och säkert! > http://www.skydrive.live.com > [[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. > > ______________________________________________ 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.