[datatable-help] zero length list component in j

[Eduard Antonyan]

Actually, looking at this example:

> dd[, ifelse(a < 2, a, integer(0)), by = a]
   a V1
1: 1  1
2: 2 NA
3: 3 NA

I don't quite understand the output. I don't have a coherent story for this
and your examples - either your second example should print NA's or this
one shouldn't have the last two rows imo.


On Fri, May 17, 2013 at 5:36 PM, Gabor Grothendieck <ggrothendieck at gmail.com
> wrote:

> Yes, I understand all that but its not inevitable that it had to be
> that way.  If we perform a computation that results in a list with
> zero length component then the corresponding row won't show up but
> another possibility might have been that it would show up filled in
> with NAs.
>
> At any rate, the question remains whether this behavior is intended or not.
>
>
>
>
>
> On Fri, May 17, 2013 at 4:47 PM, Eduard Antonyan
> <eduard.antonyan at gmail.com> wrote:
> > 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
> >> >> _______________________________________________
> >> >> datatable-help mailing list
> >> >> datatable-help at lists.r-forge.r-project.org
> >> >>
> >> >>
> >> >>
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
> >> >
> >> >
> >>
> >>
> >>
> >> --
> >> Statistics & Software Consulting
> >> GKX Group, GKX Associates Inc.
> >> tel: 1-877-GKX-GROUP
> >> email: ggrothendieck at gmail.com
> >
> >
>
>
>
> --
> Statistics & Software Consulting
> GKX Group, GKX Associates Inc.
> tel: 1-877-GKX-GROUP
> email: ggrothendieck at gmail.com
>
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