Hi David,
Besides Martins point, there is also the issue that for a lot of cases you
would still like to have the right class returned.
Right now these are returns:
> apply(matrix(NA_integer_,0,5), 1, class)
character(0)
> apply(matrix(NA_integer_,0,5), 1, identity)
integer(0)
> apply(matrix(NA,0,5), 1, identity)
logical(0)
In your case, these would all return NULL, so I think there is value in
running FUN at least once (Say if you'd want to check if FUN always returns the
right class).
And from a philosophical point of view, R is mostly a functional
programming language, I think if you want side-effects a for-loop would look
better.
Best regards,
Emil Bode
Data-analyst
+31 6 43 83 89 33
emil.b...@dans.knaw.nl
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On 30/07/2018, 11:12, "R-devel on behalf of David Hugh-Jones"
<r-devel-boun...@r-project.org on behalf of davidhughjo...@gmail.com> wrote:
Hi Martin,
Fair enough for R functions in general. But the behaviour of apply
violates
the expectation that apply(m, 1, fun) calls fun n times when m has n
rows.
That seems pretty basic.
Also, I understand from your argument why it makes sense to call apply
and
return a special result (presumably NULL) for an empty argument; but why
should apply call fun?
Cheers
David
On Mon, 30 Jul 2018 at 08:41, Martin Maechler
<maech...@stat.math.ethz.ch>
wrote:
> >>>>> David Hugh-Jones
> >>>>> on Mon, 30 Jul 2018 05:33:19 +0100 writes:
>
> > Forgive me if this has been asked many times before, but I
> > couldn't find anything on the mailing lists.
>
> > I'd expect apply(m, 1, foo) not to call `foo` if m is a
> > matrix with zero rows. In fact:
>
> > m <- matrix(NA, 0, 5)
> > apply(m, 1, function (x) {cat("Called...\n"); print(x)})
> > ## Called...
> > ## [1] FALSE FALSE FALSE FALSE FALSE
>
>
> > Similarly for apply(m, 2,...) if m has no columns. Is
> > there a reason for this?
>
> Yes :
>
> The reverse is really true for almost all basic R functions:
>
> They *are* called and give an "empty" result automatically
> when the main argument is empty.
>
> What you basicaly propose is to add an extra
>
> if(<length 0 input>)
> return(<correspondingly formatted length-0 output>)
>
> to all R functions. While that makes sense for high-level R
> functions that do a lot of things, this would really be a bad
> idea in general :
>
> This would make all of these basic functions larger {more to
maintain} and
> slightly slower for all non-zero cases just to make them
> slightly faster for the rare zero-length case.
>
> Martin Maechler
> ETH Zurich and R core Team
>
> --
Sent from Gmail Mobile
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