# diag()

**Jonathan Rougier
**
J.C.Rougier@durham.ac.uk

*Wed, 18 Aug 1999 09:26:42 +0100 (BST)*

I would like to suggest a slight modification to diag(). In the case
where x is a matrix with both row names and column names the same, it
would be reasonable if the resulting vector also had those names. I often
use diag() on variance matrices, where this modification is helpful.
The modification requires replacing
if (is.matrix(x) && nargs() == 1)
return(c(x)[1 + 0:(min(dim(x)) - 1) * (dim(x)[1] + 1)])
the first two lines, with something like
if (is.matrix(x) && nargs() == 1) {
y <- c(x)[1 + 0:(min(dim(x)) - 1) * (dim(x)[1] + 1)]
if (!is.null(nms <- dimnames(x)) && all(nms[[1]]==nms[[2]]))
names(y) <- nms[[1]]
return(y)
}
Just a thought, Jonathan.
Jonathan Rougier Science Laboratories
Department of Mathematical Sciences South Road
University of Durham Durham DH1 3LE
"[B]egin upon the precept ... that the things we see are to be
weighed in the scale with what we know" (Meredith, 1879, The Egoist)
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