The way to think about it is: prod(rep(x,n)) == x^n
and that works for n=0 too. On 1/9/06, Martin Morgan <[EMAIL PROTECTED]> wrote: > I'm a little confused. I understand that numeric(0) means an empty > numeric vector, not the number 0 expressed as numeric. As it is now, > prod(numeric(0)) generates something -- a vector of length 1 > containing the number 1 -- from nothing. I would have expected > > prod(numeric(0)) ==> numeric(0) > > this is consistent with > > numeric(0) ==> numeric(0) > numeric(0) * 1 ==> numeric(0) > cumprod(numeric(0)) ==> numeric(0) > > and, because concatenation occus before function evaluation, > > prod(c(numeric(0),1)) ==> prod( c(1) ) ==> 1 > > I would expect sum() to behave the same way, e.g., sum(numeric(0)) ==> > numeric(0). From below, > > > >>>> consider exp(sum(log(numeric(0)))) ... ?) > > >> > > >> That's a fairly standard mathematical convention, which > > >> is presumably why sum and prod work that way. > > >> > > >> Duncan Murdoch > > I would have expected numeric(0) as the result (numeric(0) is the > result from log(numeric(0)), etc). > > Martin (Morgan) > > > Martin Maechler <[EMAIL PROTECTED]> writes: > > >>>>>> "Ben" == Ben Bolker <[EMAIL PROTECTED]> > >>>>>> on Sun, 08 Jan 2006 21:40:05 -0500 writes: > > > > Ben> Duncan Murdoch wrote: > > >> On 1/8/2006 9:24 PM, Ben Bolker wrote: > > >> > > >>> It surprised me that prod(numeric(0)) is 1. I guess if > > >>> you say (operation(nothing) == identity element) this > > >>> makes sense, but ?? > > >> > > >> > > >> What value were you expecting, or were you expecting an > > >> error? I can't think how any other value could be > > >> justified, and throwing an error would make a lot of > > >> formulas more complicated. > > >> > > >>> > > >> > > >>>> consider exp(sum(log(numeric(0)))) ... ?) > > >> > > >> That's a fairly standard mathematical convention, which > > >> is presumably why sum and prod work that way. > > >> > > >> Duncan Murdoch > > > > Ben> OK. I guess I was expecting NaN/NA (as opposed to > > Ben> an error), but I take the "this makes everything else > > Ben> more complicated" point. Should this be documented or > > Ben> is it just too obvious ... ? (Funny -- I'm willing to > > Ben> take gamma(1)==1 without any argument or suggestion > > Ben> that it should be documented ...) > > > > see? so it looks to me as if you have finally convinced > > yourself that '1' is the most reasonable result.. ;-) > > > > Anyway, I've added a sentence to help(prod) {which matches > > the sentence in help(sum), BTW}. > > > > Martin > > > > ______________________________________________ > > 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 > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel