> Hi, let's say I have this > > A = matrix(c(1, 2, 4), nrow=1) > colnames(A)=c("YOO1", "YOO2", "YOO3")
Why do you need A to be a matrix and not simply a vector? > > # ie > # YOO1 YOO2 YOO3 > #[1,] 1 2 4 > > HELLO <- NULL > HELLO$YOO1="BOO" > HELLO$YOO2="BOO" > HELLO$YOO3="HOO" > Why do you need HELLO to be a list and not simply a character vector? > and I want a matrix that will sum my categorization.. how can I do it > efficiently without any loop? > > #ie BOO HOO > #[1,] 3 4 > Anyway, here is a solution: x <- tapply(A, match(unlist(HELLO), unique(unlist(HELLO))), sum) names(x) <- unique(unlist(HELLO)) x HTH, Giovanni -- Giovanni Petris <[EMAIL PROTECTED]> Associate Professor Department of Mathematical Sciences University of Arkansas - Fayetteville, AR 72701 Ph: (479) 575-6324, 575-8630 (fax) http://definetti.uark.edu/~gpetris/ ______________________________________________ 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.