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. > > Looking in the code, this makes sense: > basically (s=1; for i=0 to length(x), > multiply s by x[i]) -- which comes out to 1. > > What *should* prod(numeric(0)) produce? > I couldn't find the answer documented anywhere. > > (And how about sum(numeric(0))==0, > which for some reason makes more intuitive sense > to me, but is really exactly the same thing -- > 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 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
