Thank you for the feedback, Martin. Of course, deprecating would be a sensible way to go. I filed this issue on BugZilla under # 17198. Florent
On 22 December 2016 at 10:24, Martin Maechler <maech...@stat.math.ethz.ch> wrote: >>>>>> Florent Angly <florent.an...@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. > > yes. > > > 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 > noticeable. > > 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: > > [1] LC_COLLATE=German_Switzerland.1252 > > LC_CTYPE=German_Switzerland.1252 > > LC_MONETARY=German_Switzerland.1252 LC_NUMERIC=C > > [5] LC_TIME=German_Switzerland.1252 > > > attached base packages: > > [1] stats graphics grDevices utils datasets methods base > > > Best regards, > > > Florent > > > ______________________________________________ > > R-devel@r-project.org mailing list > > https://stat.ethz.ch/mailman/listinfo/r-devel ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
