[Rd] Unexpected I(NULL) output
florent.angly at gmail.com
Sat Dec 24 14:27:49 CET 2016
Thank you for the feedback, Martin. Of course, deprecating would be a
sensible way to go.
I filed this issue on BugZilla under # 17198.
On 22 December 2016 at 10:24, Martin Maechler
<maechler at stat.math.ethz.ch> wrote:
>>>>>> Florent Angly <florent.angly at gmail.com>
>>>>>> on Tue, 20 Dec 2016 13:42:37 +0100 writes:
> > Hi all,
> > I believe there is an issue with passing NULL to the function I().
> > class(NULL) # "NULL" (as expected)
> > print(NULL) # NULL (as expected)
> > is.null(NULL) # TRUE (as expected)
> > According to the documentation I() should return a copy of its input
> > with class "AsIs" preprended:
> > class(I(NULL)) # "AsIs" (as expected)
> > print(I(NULL)) # list() (not expected! should be NULL)
> > is.null(I(NULL)) # FALSE (not expected! should be TRUE)
> > So, I() does not behave according to its documentation.
> > In R, it is
> > not possible to give NULL attributes, but I(NULL) attempts to do that
> > nonetheless, using the structure() function. Probably:
> > 1/ structure() should not accept NULL as input since the goal of
> > structure() is to set some attributes, something cannot be done on
> > NULL.
> I tend to agree. However if we gave an error now, I notice that
> even our own code, e.g., in stats:::formula.default() would fail.
> Still, I think we should consider *deprecating* structure(NULL, *),
> so it would give a *warning* (and continue working otherwise)
> (for a while before giving an error a year later).
> > 2/ I() could accept NULL, but, as an exception, not set an "AsIs"
> > class attribute on it. This would be in line with the philosophy of
> > the I() function to return an object that is functionally equivalent
> > to the input object.
> If we'd adopt 2, the I(.) function would become slightly more
> complicated and slower... but possibly not practically
> A last option would be
> 3/ The help page for I() could note what happens in the NULL case.
> That would be the least work for everyone,
> but at the moment, I tend to agree that '1/' is worth the pain to
> have R's structure() become more consistent.
> Martin Maechler
> ETH Zurich
> > My sessionInfo() returns:
> >> sessionInfo()
> > R version 3.3.2 (2016-10-31)
> > Platform: x86_64-w64-mingw32/x64 (64-bit)
> > Running under: Windows 7 x64 (build 7601) Service Pack 1
> > locale:
> >  LC_COLLATE=German_Switzerland.1252
> > LC_CTYPE=German_Switzerland.1252
> > LC_MONETARY=German_Switzerland.1252 LC_NUMERIC=C
> >  LC_TIME=German_Switzerland.1252
> > attached base packages:
> >  stats graphics grDevices utils datasets methods base
> > Best regards,
> > Florent
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
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