R devel - Aug 2014 - RFC: diag(x, n) not preserving integer and logical x

This is not at all something new(*). As maintainer of the
Matrix  package, I don't like this inconsistency of base R's diag().
We have had the following -- forever, almost surely inherited
from S and S+  :

diag(x) preserves the storage mode of x  for  'complex' and
'double' precision,  but converts integer and logicals to double :

  > storage.mode(x <- 1i + 1:7); storage.mode(diag(x))
  [1] "complex"
  [1] "complex"
  > storage.mode(x <- 0 + 1:7);  storage.mode(diag(x))
  [1] "double"
  [1] "double"

  > storage.mode(x <- 1:7);      storage.mode(diag(x))
  [1] "integer"
  [1] "double"
  > storage.mode(x <- 1:7 > 3);  storage.mode(diag(x))
  [1] "logical"
  [1] "double"

and so it is actually a bit cumbersome (and a memory waste in
the case of large matrices) to create a diagonal integer or
logical matrix.

The help page does not mention the current behavior, though you
may say it alludes to the fact that logicals are treated as 0/1
implicitly (**)

If I change this behavior such that logical and integer x are
preserved,

	make check-all

which includes all checks, including those of all recommended
packages (including Matrix!) successfully runs through; so at
least  base + Recommended R never relies on the current
behavior, nor should any "well programmed" R code ...

Hence my proposal, somewhat tentative for now,
to change this  diag(.) behavior.

Martin Maechler

*) and possibly something we "can not" change in R, because too
   much code implicitely may be depending on it,  but now I hope
   we can still...

**) BTW, also including the somewhat amusing case of
diag(c("A","B")).

On 07/08/2014, 4:51 AM, Martin Maechler wrote:
> This is not at all something new(*). As maintainer of the
> Matrix  package, I don't like this inconsistency of base R's
diag().
> We have had the following -- forever, almost surely inherited
> from S and S+  :
> 
> diag(x) preserves the storage mode of x  for  'complex' and
> 'double' precision,  but converts integer and logicals to double :
> 
>   > storage.mode(x <- 1i + 1:7); storage.mode(diag(x))
>   [1] "complex"
>   [1] "complex"
>   > storage.mode(x <- 0 + 1:7);  storage.mode(diag(x))
>   [1] "double"
>   [1] "double"
> 
>   > storage.mode(x <- 1:7);      storage.mode(diag(x))
>   [1] "integer"
>   [1] "double"
>   > storage.mode(x <- 1:7 > 3);  storage.mode(diag(x))
>   [1] "logical"
>   [1] "double"
> 
> and so it is actually a bit cumbersome (and a memory waste in
> the case of large matrices) to create a diagonal integer or
> logical matrix.
> 
> The help page does not mention the current behavior, though you
> may say it alludes to the fact that logicals are treated as 0/1
> implicitly (**)
> 
I think the change to preserve integer makes sense, but preserving
logical does not.  A diagonal matrix has zeros off the diagonal, and
they are not logical.  Having diag() sometimes return a matrix with
FALSE off the diagonal just looks wrong.

Duncan Murdoch
> If I change this behavior such that logical and integer x are
> preserved,
> 
> 	make check-all
> 
> which includes all checks, including those of all recommended
> packages (including Matrix!) successfully runs through; so at
> least  base + Recommended R never relies on the current
> behavior, nor should any "well programmed" R code ...
> 
> Hence my proposal, somewhat tentative for now,
> to change this  diag(.) behavior.
> 
> Martin Maechler
> 
> *) and possibly something we "can not" change in R, because too
>    much code implicitely may be depending on it,  but now I hope
>    we can still...
> 
> **) BTW, also including the somewhat amusing case of
diag(c("A","B")).
> 
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