[Rd] NROW and NCOL on NULL

[Martin Maechler]

>>>>> Simone Giannerini 
>>>>>     on Sun, 24 Sep 2023 16:57:00 +0200 writes:

    > Thank you for your comment, On Sat, Sep 23, 2023 at
    > 9:51 PM Ben Bolker <bbolker using gmail.com> wrote:
    >> 
    >> This is certainly worth discussing, but there's always a
    >> heavy burden of back-compatibility; how much better would
    >> it be for NCOL and NROW to both return zero, vs. the
    >> amount of old code that would be broken?

    > I do not have an answer to this question but it seems to
    > me that code that relies upon NCOL(NULL) being 1 is not
    > extremely good (and portable).

Well, it remains *very* portable,  as long as we keep the behavior.
It has worked as it does for more than twenty years, and if you
finally remain convinced that we won't change, it will remain portable
between all versions of R from the very old past to the remote
future  ... ;-)

Martin


    >> Furthermore, the reason for this behaviour is justified
    >> as consistency with the behaviour of as.matrix() and
    >> cbind() for zero-length vectors, from ?NCOL:
    >> 
    >> ## as.matrix() produces 1-column matrices from 0-length
    >> vectors, ## and so does cbind() :
    >> 
    >> (of course you could argue that this behaviour should be
    >> changed as well ...)
    >> 
    >> 

    > Yes, it is documented and somehow clashes with the more
    > intuitive behaviour of subsetting matrices

    >> a <- matrix(1:4,2,2) a
    >      [,1] [,2] [1,] 1 3 [2,] 2 4
    >> a2 <- a[,-(1:2)] a2

    > [1,] [2,]
    >> dim(a2)
    > [1] 2 0

    > NULL is often used to declare an undefined value for the
    > argument of a function. If such an argument is potentially
    > a matrix, then using NULL as the default requires
    > additional code to check for the number of columns and use
    > it in the code.  The same holds to a lesser extent for
    > functions that are expected to return a matrix and return
    > NULL instead.

    > Kind regards,

    > Simone

    >> On 2023-09-23 3:41 p.m., Simone Giannerini wrote: > I
    >> know it's documented and I know there are other ways to
    >> guard > against this behaviour, once you know about this.
    >> > The point is whether it might be worth it to make NCOL
    >> and NROW return > the same value on NULL and make R more
    >> consistent/intuitive and > possibly less error prone.
    >> >
    >> > Regards,
    >> >
    >> > Simone
    >> >
    >> > On Sat, Sep 23, 2023 at 7:50 PM Duncan Murdoch
    >> <murdoch.duncan using gmail.com> wrote:
    >> >>
    >> >> It's been documented for a long time that NCOL(NULL)
    >> is 1.  What >> particular problems did you have in mind?
    >> There might be other ways to >> guard against them.
    >> >>
    >> >> Duncan Murdoch
    >> >>
    >> >> On 23/09/2023 1:43 p.m., Simone Giannerini wrote: >>>
    >> Dear list,
    >> >>>
    >> >>> I do not know what would be the 'correct' answer to
    >> the following but >>> I think that they should return the
    >> same value to avoid potential >>> problems and hard to
    >> debug errors.
    >> >>>
    >> >>> Regards,
    >> >>>
    >> >>> Simone
    >> >>> ---------------------------------------
    >> >>>
    >> >>>> NCOL(NULL) >>> [1] 1
    >> >>>
    >> >>>> NROW(NULL) >>> [1] 0
    >> >>>
    >> >>>> sessionInfo() >>> R version 4.3.1 RC (2023-06-08
    >> r84523 ucrt) >>> Platform: x86_64-w64-mingw32/x64
    >> (64-bit) >>> Running under: Windows 11 x64 (build 22621)
    >> >>>
    >> >>> Matrix products: default
    >> >>>
    >> >>>
    >> >>> locale: >>> [1] LC_COLLATE=Italian_Italy.utf8
    >> LC_CTYPE=Italian_Italy.utf8 >>> [3]
    >> LC_MONETARY=Italian_Italy.utf8 LC_NUMERIC=C >>> [5]
    >> LC_TIME=Italian_Italy.utf8
    >> >>>
    >> >>> time zone: Europe/Rome >>> tzcode source: internal
    >> >>>
    >> >>> attached base packages: >>> [1] stats graphics
    >> grDevices utils datasets methods base
    >> >>>
    >> >>> loaded via a namespace (and not attached): >>> [1]
    >> compiler_4.3.1
    >> >>>
    >> >>
    >> >
    >> >
    >> 
    >> ______________________________________________
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    >> https://stat.ethz.ch/mailman/listinfo/r-devel



    > -- 
    > ___________________________________________________

    > Simone Giannerini Dipartimento di Scienze Statistiche
    > "Paolo Fortunati" Universita' di Bologna Via delle belle
    > arti 41 - 40126 Bologna, ITALY Tel: +39 051 2098262 Fax:
    > +39 051 232153 https://simonegiannerini.net/

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