[Rd] apply with zero-row matrix
David Hugh-Jones
d@vidhughjone@ @ending from gm@il@com
Mon Jul 30 17:12:44 CEST 2018
Interesting discussion. I'm not wholly convinced by Martin's and Emil's
arguments. The behaviour seems to violate an obvious expectation (fun is
called once per row) to satisfy a subtle one (result has a guaranteed
dimension and type).
In any case, here's a suggested chunk of rd to go at the end of the "Value":
If \code{dim(X)[MARGIN]} is zero, then \code{FUN} is called once, with an
argument of the appropriate dimensions. The argument's type is the same as
\code{typeof(m)}, and the argument values are those returned by
\code{vector(typeof(m))}. For example, if m is numeric, the argument will
be a vector (or matrix or array) of zeroes. The type and length of the
value returned by \code{FUN} is used to determine the type of the result.
And at the end of "Details":
\code{FUN} is always called at least once, see below.
David
On Mon, 30 Jul 2018 at 15:05, Gabor Grothendieck <ggrothendieck using gmail.com>
wrote:
> Try pmap and related functions in purrr:
>
> pmap(as.data.frame(m), ~ { cat("Called...\n"); print(c(...)) })
> ## list()
>
> On Mon, Jul 30, 2018 at 12:33 AM, David Hugh-Jones
> <davidhughjones using gmail.com> wrote:
> > 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? Could it be documented?
> >
> > David
> > --
> > Sent from Gmail Mobile
> >
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> >
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>
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