The shortest expression I can think of is:
as.numeric(interaction(mat[,1],mat[,2],drop=T)) Completing the thought of those who suggested dist or unique: N <- nrow(mat) dd <- as.matrix(dist(rbind(mat,unique(mat))))[-seq(N),seq(N)] apply(dd,2,function(x)match(0,x)) Scott Waichler <scott.waichler <at> pnl.gov> writes: : : I would like to generate a vector having the same length : as the number of rows in a matrix. The vector should contain : an integer indicating the "group" of the row, where identical : matrix rows are in a group, and a unique row has a unique integer. : Thus, for : : a <- c(1,2) : b <- c(1,3) : c <- c(1,2) : d <- c(1,2) : e <- c(1,3) : f <- c(2,1) : mat <- rbind(a,b,c,d,e,f) : : I would like to get the vector c(1,2,1,1,2,3). I know dist() gives : part of the answer, but I can't figure out how to use it for : this purpose without doing a lot of looping. I need to apply this : to matrices up to ~100000 rows. : : Thanks, : Scott Waichler : Pacific Northwest National Laboratory : scott.waichler_at_pnl.gov ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
