[Rd] dim<-() changed in R-devel; no longer removing "dimnames" when doing dim(x) <- dim(x)

[Martin Maechler]

>>>>> Hervé Pagès 
>>>>>     on Mon, 30 Oct 2023 17:17:47 -0700 writes:

    > Hi Martin, Henrik, I actually like this change.


    > Makes a lot of sense IMO that dim(x) <- dim(x) be a no-op,
    > or, more generally, that foo(x) <- foo(x) be a no-op for
    > any setter/getter combo.

yes.
For me, another "strong" reason for a change was that I could
add {or modify more generally} the *names* of dim(.)  --- and
believe me, these can be somewhat "handy" when you a relatively
large simulation result array `ANS` say where
length(dim(ANS)) is 4 or 5.

Still, I've reverted the change for now, as it needed more
discussion etc and was unplanned for.

So, now, again,

  A <- array(1:120, c(2,3,4,5),
            dimnames = list(c("N1", "N2"), LETTERS[1:3], NULL, NULL))
  str(A)
  # int [1:2, 1:3, 1:4, 1:5] 1 2 3 4 5 6 7 8 9 10 ...
  # - attr(*, "dimnames")=List of 4
  #  ..$ : chr [1:2] "N1" "N2"
  #  ..$ : chr [1:3] "A" "B" "C"
  #  ..$ : NULL
  #  ..$ : NULL

 names(dim(A)) <- c("SSize", "Kind", "method", "rep")
 dim(A) # is nice ..
 # SSize   Kind method    rep 
 #     2      3      4      5 

 dimnames(A) #  *but* is lost (again, after my revert)


    > FWIW S4Arrays::set_dim() does that too. It also preserves
    > the dimnames if the right value is only adding or dropping
    > outermost (ineffective) dimensions:

    >> x <- array(1:6, dim=c(2,3,1), dimnames=list(c("A", "B"), c("x","y", "z"), "T"))
    >> S4Arrays:::set_dim(x, 2:3)
    >   x y z
    > A 1 3 5
    > B 2 4 6

    > Note that this is consistent with drop().

Yes, that's nice  ... and the drop() consistency is an extra.
Martin

    > Best,

    > H.


    > On 10/30/23 03:53, Martin Maechler wrote:
    >>>>>>> Henrik Bengtsson
    >>>>>>> on Sun, 29 Oct 2023 10:42:19 -0700 writes:
    >> > Hello,
    >> 
    >> > the fix of PR18612
    >> > (https://bugs.r-project.org/show_bug.cgi?id=18612) in
    >> > r85380
    >> > (https://github.com/wch/r-source/commit/2653cc6203fce4c48874111c75bbccac3ac4e803)
    >> > caused a change in `dim<-()`.  Specifically, in the past,
    >> > any `dim<-()` assignment would _always_ remove "dimnames"
    >> > and "names" attributes per help("dim"):
    >> 
    >> 
    >> >     The replacement method changes the "dim" attribute
    >> > (provided the new value is compatible) and removes any
    >> > "dimnames" and "names" attributes.
    >> 
    >> > In the new version, assigning the same "dim" as before
    >> > will no longer remove "dimnames".  I'm reporting here to
    >> > check whether this change was intended, or if it was an
    >> > unintended side effect of the bug fix.
    >> 
    >> > For example, in R Under development (unstable) (2023-10-21
    >> > r85379), we would get:
    >> 
    >> >> x <- array(1:2, dim=c(1,2), dimnames=list("A",
    >> >> c("a","b"))) str(dimnames(x))
    >> > List of 2 $ : chr "A" $ : chr [1:2] "a" "b"
    >> 
    >> >> dim(x) <- dim(x) ## Removes "dimnames" no matter what
    >> >> str(dimnames(x))
    >> >  NULL
    >> 
    >> 
    >> > whereas in R Under development (unstable) (2023-10-21
    >> > r85380) and beyond, we now get:
    >> 
    >> >> x <- array(1:2, dim=c(1,2), dimnames=list("A",
    >> >> c("a","b"))) str(dimnames(x))
    >> > List of 2 $ : chr "A" $ : chr [1:2] "a" "b"
    >> 
    >> >> dim(x) <- dim(x) ## No longer removes "dimnames"
    >> >> str(dimnames(x))
    >> > List of 2 $ : chr "A" $ : chr [1:2] "a" "b"
    >> 
    >> >> dim(x) <- rev(dim(x)) ## Still removes "dimnames"
    >> >> str(dimnames(x))
    >> >  NULL
    >> 
    >> > /Henrik
    >> 
    >> Thank you, Henrik.
    >> 
    >> This is "funny" (in an unusal sense):
    >> indeed, the change was *in*advertent, by me (svn rev 85380).
    >> 
    >> I had experimentally {i.e., only in my own private version of R-devel!}
    >> modified the behavior of `dim<-` somewhat
    >> such it does *not* unnecessarily drop dimnames,
    >> e.g., in your   `dim(x) <- dim(x)` case above,
    >> one could really argue that it's a "true loss" if x loses
    >> dimnames "unnecessarily" ...
    >> 
    >> OTOH, I knew in the mean time that  `dim<-` has always been
    >> documented to drop dimnames in all cases,  and even more
    >> importantly, I got a strong recommendation to *not* go further
    >> with this idea -- not only for back compatibility reasons, but
    >> also for internal logical consistency.
    >> 
    >> Most probably, we will just revert this inadvertent change,
    >> but before that ... since it has been out in the wild anyway,
    >> we could quickly consider if it *did* break code.
    >> 
    >> I assume it did, or you would not have noticed ?
    >> 
    >> Martin
    >> 
    >> ______________________________________________
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    > -- 
    > Hervé Pagès

    > Bioconductor Core Team
    > hpages.on.github using gmail.com

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