[Rd] RFC: diag(x, n) not preserving integer and logical x

[Duncan Murdoch]

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")).
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>