But this thread seems to have pointed to some inconsistencies:
> cumprod( numeric(0) )
numeric(0)
> cumsum( numeric(0) )
numeric(0)
shouldn't this give the same as prod() and sum()
in this case?
Same with cummin() and cummax().
Kjetil
On 1/9/06, Duncan Murdoch <[EMAIL PROTECTED]> wrote:
>
> On 1/9/2006 12:40 PM, Martin Morgan 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,
> >
>
> I think the code below works as I'd expect. Would you really like the
> last answer to be numeric(0)?
>
> > x <- 1:10
> > sum(x)
> [1] 55
> > sum(x[x>5])
> [1] 40
> > sum(x[x>10])
> [1] 0
>
> Duncan Murdoch
>
> >> >>>> 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
>
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