Message-ID: <bd6150f0-c23d-741f-13c0-cf0f31228b2b@sapo.pt>
Date: 2018-08-05T05:57:38Z
From: Rui Barradas
Subject: Is this a bug in `[`?
In-Reply-To: <CAPekMCkyF5f90dXLh6WJZwqXpKPbrg2sLrN-DdjqAoxXGbCtXA@mail.gmail.com>
Thanks.
This is exactly the doubt I had.
Rui Barradas
?s 05:26 de 05/08/2018, Kenny Bell escreveu:
> This should more clearly illustrate the issue:
>
> c(1, 2, 3, 4)[-seq_len(4)]
> #> numeric(0)
> c(1, 2, 3, 4)[-seq_len(3)]
> #> [1] 4
> c(1, 2, 3, 4)[-seq_len(2)]
> #> [1] 3 4
> c(1, 2, 3, 4)[-seq_len(1)]
> #> [1] 2 3 4
> c(1, 2, 3, 4)[-seq_len(0)]
> #> numeric(0)
> Created on 2018-08-05 by the reprex package (v0.2.0.9000).
>
> On Sun, Aug 5, 2018 at 3:58 AM Rui Barradas <ruipbarradas at sapo.pt
> <mailto:ruipbarradas at sapo.pt>> wrote:
>
>
>
> ?s 15:51 de 04/08/2018, I?aki ?car escreveu:
> > El s?b., 4 ago. 2018 a las 15:32, Rui Barradas
> > (<ruipbarradas at sapo.pt <mailto:ruipbarradas at sapo.pt>>) escribi?:
> >>
> >> Hello,
> >>
> >> Maybe I am not understanding how negative indexing works but
> >>
> >> 1) This is right.
> >>
> >> (1:10)[-1]
> >> #[1]? 2? 3? 4? 5? 6? 7? 8? 9 10
> >>
> >> 2) Are these right? They are at least surprising to me.
> >>
> >> (1:10)[-0]
> >> #integer(0)
> >>
> >> (1:10)[-seq_len(0)]
> >> #integer(0)
> >>
> >>
> >> It was the last example that made me ask, seq_len(0) whould avoid an
> >> if/else or something similar.
> >
> > I think it's ok, because there is no negative zero integer, so -0
> is 0.
>
> Ok, this makes sense, I should have thought about that.
>
> >
> > 1.0/-0L # Inf
> > 1.0/-0.0 # - Inf
> >
> > And the same can be said for integer(0), which is the result of
> > seq_len(0): there is no negative empty integer.
>
> I'm not completely convinced about this one, though.
> I would expect -seq_len(n) to remove the first n elements from the
> vector, therefore, when n == 0, it would remove none.
>
> And integer(0) is not the same as 0.
>
> (1:10)[-0] == (1:10)[0] == integer(0) # empty
>
> (1:10)[-seq_len(0)] == (1:10)[-integer(0)]
>
>
> And I have just reminded myself to run
>
> identical(-integer(0), integer(0))
>
> It returns TRUE so my intuition is wrong, R is right.
> End of story.
>
> Thanks for the help,
>
> Rui Barradas
>
> >
> > I?aki
> >
> >>
> >>
> >> Thanks in advance,
> >>
> >> Rui Barradas
> >>
> >> ______________________________________________
> >> R-devel at r-project.org <mailto:R-devel at r-project.org> mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-devel
>
> ______________________________________________
> R-devel at r-project.org <mailto:R-devel at r-project.org> mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>