On Thu, Apr 21, 2011 at 12:52:34PM -0700, Kehl Dániel wrote: > Thank you. > I only need those where the rowsum = n. > I could choose those with code, but I dont think it is efficient that way.
Efficiency of using expand.grid() may be improved, if expand.grid() is used only to k-1 columns, then the k-th column is computed and the rows with a negative value in it are discarded. n <- 6 k <- 3 a <- as.matrix(expand.grid(rep(list(0:n), k - 1))) a <- cbind(a, n - rowSums(a)) colnames(a) <- NULL a <- a[0 <= a[, k], ] nrow(a) == choose(n + k - 1, k - 1) [1] TRUE In this way, we select choose(n + k - 1, k - 1) among n^(k - 1) rows and not among n^k. Hope this helps. Petr Savicky. ______________________________________________ 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.
