[Rd] extract function "[" and empty index
lgautier at gmail.com
Sun Mar 9 19:29:32 CET 2008
Thanks, I was forgetting the recycling rule.
2008/3/9, Gabor Grothendieck <ggrothendieck at gmail.com>:
> Use TRUE.
> On Sun, Mar 9, 2008 at 5:05 AM, Laurent Gautier <lgautier at gmail.com> wrote:
> > Dear list,
> > I am having a question regarding the extract function "[".
> > The man page says that one usage with k-dimensional arrays is to
> > specify k indices to "[", with an empty index indicating that all
> > entries in that dimension are selected.
> > The question is the following: is there an R object qualifying as an
> > "empty index" ? I understand that the lazy evaluation of parameters
> > allows one to
> > have genuinely missing parameters, but I would like to have an object
> > instead. I understand that one can always have an if/else workaround,
> > but I thought should ask, just in case.
> > I tried with NULL but with little success, as it appears to give the
> > same results
> > as an empty vector.
> > > m = matrix(1, 2, 2)
> > > m[1, NULL]
> > numeric(0)
> > > m[1, integer(0)]
> > numeric(0)
> > Since I was at it, I noted that the result obtained with "numeric(0)"
> > definitely makes sense but could as well be seen as challenging the
> > concept of an empty index presented in the man page (One could somehow
> > expect the presence of an object meaning "everything" rather than
> > "missingness" meaning it).
> > Thanks,
> > Laurent
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
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