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 <ruipbarra...@sapo.pt> wrote: > > > Às 15:51 de 04/08/2018, Iñaki Úcar escreveu: > > El sáb., 4 ago. 2018 a las 15:32, Rui Barradas > > (<ruipbarra...@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 > >> > >> ______________________________________________ > >> R-devel@r-project.org mailing list > >> https://stat.ethz.ch/mailman/listinfo/r-devel > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
