I just thought that returning a more accurate result was better and that (1:10)/10 was an obvious way to calculate. It turned out that it was not that easy.
I found that calculation that I proposed previously was not accurate for seq(-5, 5, length=101). I then thought of from + (0:(length.out - 1))/((length.out - 1)/(to - from)) , that is dividing by (1/by) instead of multiplying by 'by'. But I then found that 1/(1/49) didn't give 49. So, now I am proposing dividing by (1/by) selectively, like from + if (abs(to - from) < length.out - 1 && abs(to - from) >= 2^(-22) # exact with 16 significant digits ) (0:(length.out - 1))/((length.out - 1)/(to - from)) else (0:(length.out - 1))*((to - from)/(length.out - 1)) Not changing 'seq.default' is fine, too. -------------------------------------------- On Sat, 8/9/18, Gabe Becker <becker.g...@gene.com> wrote: Subject: Re: [Rd] Proposal: more accurate seq(from, to, length=n) Cc: "r-devel" <r-devel@r-project.org> Date: Saturday, 8 September, 2018, 5:38 AM Suharto, My 2c inline. On Fri, Sep 7, 2018 at 2:34 PM, Suharto Anggono Suharto Anggono via R-devel <r-devel@r-project.org> wrote: In R, seq(0, 1, 0.1) gives the same result as (0:10)*0.1. It is not the same as c(0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1) , as 0.1 is not represented exactly. I am fine with it. In R, seq(0, 1, length=11) gives the same result as seq(0, 1, 0.1). However, for seq(0, 1, length=11), it is more accurate to return c(0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1) . It can be obtained by (0:10)/10. When 'from', 'to', and 'length.out' are specified and length.out > 2, I propose for function 'seq.default' in R to use something like from + ((0:(length.out - 1))/(length.out - 1)) * (to - from) instead of something like from + (0:(length.out - 1)) * ((to - from)/(length.out - 1)) . In your example case under 3.50 on my system these two expressions give results which return TRUE from all.equal, which is the accepted way of comparing non-integer numerics in R for "sameness". > from = 0 > to = 1 > length.out = 11 > all.equal(from + ((0:(length.out - 1))/(length.out - 1)) * (to - from), from + (0:(length.out - 1)) * ((to - from)/(length.out - 1))) [1] TRUE Given that I'm wondering what the benefit you're looking for here is that would outweigh the very large set of existing code whose behavior would technically change under this change. Then again, it wouldn't change with respect to the accepted all.equal test, so I guess you could argue that either there's "no change" or the change is ok? I'd still like to know what practical problem you're trying to solve though. if you're looking for the ability to use == to compare non integer sequences generated different ways, as far as I understand the answer is that you shouldn't be expecting to be able to do that. Best,~G ______________________________ ________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/ listinfo/r-devel -- Gabriel Becker, Ph.DScientistBioinformatics and Computational BiologyGenentech Research ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
