[datatable-help] zero length list component in j

[Gabor Grothendieck]

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