Hi,
On 2/2/07, Martin Olivier <[EMAIL PROTECTED]> wrote: > > Hi all, > > Suppose I have a vector x with numerical values. > In y, I have a categorial variable : y<-c(1,1,..2,2,...30,30,30) > x and y have the same length. > I would like to compute the mean for x for the modality 1 to 30 in y. > mean(x[y==1]),...,mean(x[y==30]) I hope I understand your question correctly, but is this what you are looking for? x <- runif(10000) y <- sample(x=1:30, size=length(x), replace=TRUE) one.possibility <- tapply(X=x, INDEX=list(my.categ.var=y), FUN=mean) another.possibility <- by(data=x, INDICES=list(my.categ.var=y), FUN=mean) one.possibility another.possibility Which one you prefer depends probably on your taste and what you intend to do with the results. HTH, Roland [[alternative HTML version deleted]] ______________________________________________ R-help@stat.math.ethz.ch 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.