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
>
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