On Mon, Dec 20, 2010 at 11:04 AM, cory n <corynis...@gmail.com> wrote: >> length(sample(25000, 25000*(1-.55))) > [1] 11249 > >> 25000*(1-.55) > [1] 11250 > >> length(sample(25000, 11250)) > [1] 11250 > >> length(sample(25000, 25000*.45)) > [1] 11250 > > So the question is, why do I get 11249 out of the first command and not > 11250? I can't figure this one out.
Let me make a wild guess: > floor(25000*(1-.55)) [1] 11249 > 25000*(1-.55) [1] 11250 > 25000*(1-.55) - 11250 [1] -1.818989e-12 > 25000*0.45 - 11250 [1] 0 I'm guessing that the machine representation of 0.55 is off by something like 1e-16, which gets multiplied by a lot (25000) and this is enough for the floor (or whatever rounding the internal code uses) to make it 11249. The morale of the story is do not multiply non-exact numbers by huge constants or you may get small inaccuracies. Peter ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
