[datatable-help] .SD without by seems to fail

[Chris Neff]

I think the original example should be able to work.  There are times
where I am dynamically building the by list based on the number of
subslice keys I have for my data.table. Sometimes I have to aggregate
over a certain key, so if my keys are "x" and "y" and I have value
columns V1, V2, V3 I will do something like:

by.cols = setdiff(key(DT), "x")
DT[, sum(V1), by=by.cols]

Now if I only have one key column "x", I want this to aggregate over
the whole data.table. This in the past didn't work until I submitted a
bug report and it was fixed, but I never have had to do it with the
whole .SD.  But I could easily see wanting to do

DT[, lapply(.SD, sum), by=by.cols]

especially if I include .SDcols with it too.  And I don't want to have
to check for an empty by.cols and do some different code just for that
case.  It makes sense to have it all consistent.


2012/1/9 Timothée Carayol <timothee.carayol at gmail.com>:
> as.data.table(lapply(DT, sum)) works and doesn't seem much less elegant?
>
> (Well -- it would work if you were not trying to take the sum of a factor
> ;-))
>
> t
>
> On Mon, Jan 9, 2012 at 4:45 PM, Joseph Voelkel <jgvcqa at rit.edu> wrote:
>>
>> # from  help(data.table)
>>
>> DT = data.table(x=rep(c("a","b","c"),each=3), y=c(1,3,6), v=1:9)
>>
>> DT[,lapply(.SD,sum),by=x]  # this works fine
>>
>>
>>
>> # but this fails
>>
>> DT[,lapply(.SD,sum)]
>>
>> # with this message: Error in lapply(.SD, sum) : object '.SD' not found
>>
>>
>>
>> # Am I missing something obvious here?
>>
>>
>>
>>
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>
>
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