# [R] Constructing correlation matrices

Horace Tso Horace.Tso at pgn.com
Mon Jul 30 23:41:12 CEST 2007

```Greg,

I take it that you're trying to generate a random correlation matrix, so first create a covariance matrix,

p = 6
v = matrix(rnorm(p*p), ncol=p)
cov = t(v) %*% v

Then convert it to a correlation matrix,

cov2cor(cov)

HTH.

Horace

>>> Gregory Gentlemen <gregory_gentlemen at yahoo.ca> 7/29/2007 7:31:36 PM >>>
Greetings,

I have a seemingly simple task which I have not been able to solve today and I checked all of the help archives on this and have been unable to find anything useful. 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

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