[Rd] Is this a bug in `[`?

[Rui Barradas]

Thanks,

This is what I needed.
I had read the R Inferno a long time ago and apparently forgot this one.

Rui Barradas

Às 08:46 de 05/08/2018, Patrick Burns escreveu:
> This is Circle 8..1.13 of the R Inferno.
> 
> 
> On 05/08/2018 06:57, Rui Barradas wrote:
>> Thanks.
>> This is exactly the doubt I had.
>>
>> Rui Barradas
>>
>> Às 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 using sapo.pt 
>>> <mailto:ruipbarradas using sapo.pt>> wrote:
>>>
>>>
>>>
>>>     Às 15:51 de 04/08/2018, Iñaki Úcar escreveu:
>>>      > El sáb., 4 ago. 2018 a las 15:32, Rui Barradas
>>>      > (<ruipbarradas using sapo.pt <mailto:ruipbarradas using sapo.pt>>) escribió:
>>>      >>
>>>      >> 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
>>>
>>>      >
>>>      > Iñaki
>>>      >
>>>      >>
>>>      >>
>>>      >> Thanks in advance,
>>>      >>
>>>      >> Rui Barradas
>>>      >>
>>>      >> ______________________________________________
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