[Rd] extract function "[" and empty index

[Laurent Gautier]

Thanks, I was forgetting the recycling rule.


L.


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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