[datatable-help] zero length list component in j

[Eduard Antonyan]

well numeric(0) is no data, but because in the first case there was other
data to output and you also asked to output `y`, what else was it supposed
to do? ( it might help to look at the output of c(numeric(0), numeric(0)) )


On Fri, May 17, 2013 at 3:38 PM, Gabor Grothendieck <ggrothendieck at gmail.com
> wrote:

> In the first case it replaced the zero length component with NA and in
> the second case it did not.  Why the difference?
>
> On Fri, May 17, 2013 at 4:33 PM, Eduard Antonyan
> <eduard.antonyan at gmail.com> wrote:
> > Maybe I'm missing smth, but what else did you expect? Looks like it did
> it's
> > best to compensate for the user not supplying full data in the first
> > example, and there really was nothing to do in the second one.
> >
> >
> >
> > On Fri, May 17, 2013 at 3:27 PM, Gabor Grothendieck
> > <ggrothendieck at gmail.com> wrote:
> >>
> >> Is this intended?  If we use j = list(x = "X", y = numeric(0)) we get
> >> a row but if we use just list(y = numeric(0)) then we do not get a
> >> row.  In the first case it filled in the zero length component with NA
> >> and in the second case it just omitted the row entirely:
> >>
> >> > dd <- data.table(a = 1:3)
> >> > dd
> >>    a
> >> 1: 1
> >> 2: 2
> >> 3: 3
> >> > dd[, list(x = "X", y = numeric(0)), by = a]
> >>    a x  y
> >> 1: 1 X NA
> >> 2: 2 X NA
> >> 3: 3 X NA
> >> > dd[, list(y = numeric(0)), by = a]
> >> Empty data.table (0 rows) of 2 cols: a,y
> >>
> >>
> >> --
> >> Statistics & Software Consulting
> >> GKX Group, GKX Associates Inc.
> >> tel: 1-877-GKX-GROUP
> >> email: ggrothendieck at gmail.com
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> >> datatable-help mailing list
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> >>
> >>
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> >
> >
>
>
>
> --
> Statistics & Software Consulting
> GKX Group, GKX Associates Inc.
> tel: 1-877-GKX-GROUP
> email: ggrothendieck at gmail.com
>
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