NROW and NCOL on NULL

Thank you for your comment,
    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).
   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 at 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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___________________________________________________

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/

NROW and NCOL on NULL

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