Is this a bug in `[`?

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

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