diag() has a bug (PR#13702)

The intent of diag(foo, 2, 2) was to return a matrix that is a 2 x 2  
matrix which contains only the diagonal entries of the matrix foo.   
I can't do diag(foo) because this returns a vector.  I could reach  
my goal with matrix(diag(foo), nrow = nrow(foo), ncol = ncol(foo)).   
If this is not a reasonable thing for diag(<matrix>, <numeric>,  
<numeric>) to return, then at the very least the error message  
should be changed, as the first argument is in fact a matrix.

On Thu, May 14, 2009 at 3:24 PM, Benilton Carvalho  
<bcarvalh at jhsph.edu> wrote:
My understanding is that providing nrow and ncol, you want to create  
a diagonal matrix with those dimensions.

diag(pi, 6, 6)

and that by

diag(foo, 2, 2)

you really meant

diag(foo)[2]

Apologies if I misunderstood.

b

On May 14, 2009, at 10:45 AM, michael.m.spiegel at gmail.com wrote:

Full_Name: Michael Spiegel
Version: 2.9.0
OS: linux
Submission from: (NULL) (204.111.252.142)


The diag() function appears to reject the first argument when it is  
a matrix,
and nrow and ncol arguments are also provided.

foo <- matrix(c(1:4),2,2)
foo
   [,1] [,2]
[1,]    1    3
[2,]    2    4
diag(foo)
[1] 1 4
diag(foo, 2, 2)
Error in diag(foo, 2, 2) : first argument is array, but not matrix.
is.matrix(foo)
[1] TRUE