See ?dist for an object oriented approach that may be better. Directly, you can do something like (see ?row ?col):
x <- matrix(NA, 10,10) ## Lower triangular : x[row(x) >= col(x) ] <- rnorm(55) x[row(x) < col(x)] <- x[row(x) > col(x)] ## or you could have saved the random vector and re-used it. Bert Gunter Genentech Nonclinical Statistics -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Gregory Gentlemen Sent: Friday, July 27, 2007 8:28 PM To: r-help@stat.math.ethz.ch Subject: [R] generating symmetric matrices Greetings, I have a seemingly simple task which I have not been able to solve today. I want to construct a symmetric matrix of arbtriray size w/o using loops. The following I thought would do it: p <- 6 Rmat <- diag(p) dat.cor <- rnorm(p*(p-1)/2) Rmat[outer(1:p, 1:p, "<")] <- Rmat[outer(1:p, 1:p, ">")] <- dat.cor However, the problem is that the matrix is filled by column and so the resulting matrix is not symmetric. I'd be grateful for any adive and/or solutions. Gregory --------------------------------- [[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. ______________________________________________ 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.
