[R] rownames cannot allocate vector of size

[Larson, TR]

Hi,

On R 2.10.1 for Windows, when I do the following to duplicate the 
structure of a large numeric matrix called matrix1:

matrix2 <- matrix(0,nrow=nrow(matrix1),ncol=ncol(matrix1))

and then

rownames(matrix2) <- rownames(matrix1)

I get a "cannot allocate vector of size xxMb" error

but if I instead do:

rnames <- list()
rnames <- rownames(matrix1)
matrix2 <- matrix(0,nrow=nrow(matrix1),ncol=ncol(matrix1),dimnames=rnames)

I get no error.

Of course both approaches work in R on Unix without memory limits.  But 
I'm intrigued about the apaprent difference in memory usage/allocation 
for the two above approaches. Is there any explanation for this 
difference in behaviour?

thanks
Tony