>>>>> 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
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