Hi Todd, Here is a function that was suggested to me by Gabor Grothendieck. This function counts the number of times each row of a matrix B occurs in another matrix A.
rowmatch.count <- function(a,b) { f <- function(...) paste(..., sep=":") a2 <- do.call("f", as.data.frame(a)) b2 <- do.call("f", as.data.frame(b)) c(table(c(a2,unique(b2)))[b2] - 1) } If you are interested in finding the number of occurrences of a vector "b" instead, you can call this function as follows: rowmatch.count(A,t(as.matrix(b)) Hope this is helps, Ravi. > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:r-help- > [EMAIL PROTECTED] On Behalf Of Todd Remund > Sent: Monday, August 15, 2005 1:13 AM > To: r-help@stat.math.ethz.ch > Subject: [R] Vector comparison to matrix > > I am looking for a fast way to count the number of rows in a matrix are > identical to a pattern vector. For example, if I am interested in > counting > the number of row vectors in a matrix that are identical to (1,2,3) what > would I do? I have tried the identical statement in a loop but this is > far > too slow. I have a very large matrix and need to avoid loops at all > costs. > Thanks for any help. > Todd Remund > > ______________________________________________ > 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 ______________________________________________ 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