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

[Matthew Dowle]

Now fixed in v1.8.1 :

o  .N, .SD and .BY are now available to j when 'by' is missing, "", 
   character() and NULL, fixing #1732. For consistency so that j works
   unchanged when by is dynamic and passed one of those values all
   meaning 'don't group'. Thanks to Joseph Voelkel reporting and Chris 
   Neff for further use cases. Tests added.

o  0 length by (such as NULL and character(0)) now return a data.table 
   when j is vector, rather than vector, for consistency of return    
   types when by is dynamic and 'dont group' needs to be represented. 
   Bug fix #1599 in v1.7.0 was fixing an error in this case (0 length 
   by).

On Wed, 2012-01-11 at 21:22 +0000, Matthew Dowle wrote:
> Thanks. .N and .BY added to FR#1732.
> 
> On Tue, 2012-01-10 at 17:28 -0500, Joseph Voelkel wrote:
> > Same issue with .N and .BY, not surprisingly.
> > 
> > Regarding
> >   "as.data.table(lapply(DT, sum)) works and doesn't seem much less elegant?"
> > 
> > In my example, I was writing several statements of .SD with by=, and then wanted a statement
> > Without the by=. It just seemed that I shouldn't need to change .SD to DT ... Same fundamental point as Chris's but not is as elegant a context.
> > 
> > 
> > -----Original Message-----
> > From: Matthew Dowle [mailto:mdowlenoreply at virginmedia.com] On Behalf Of Matthew Dowle
> > Sent: Monday, January 09, 2012 5:15 PM
> > To: Chris Neff
> > Cc: timothee.carayol at gmail.com; Joseph Voelkel; datatable-help at lists.r-forge.r-project.org
> > Subject: Re: [datatable-help] .SD without by seems to fail
> > 
> > Ok, very persuasive. I've raised a bug report :
> > 
> > https://r-forge.r-project.org/tracker/index.php?func=detail&aid=1732&group_id=240&atid=975
> > 
> > 
> > On Mon, 2012-01-09 at 14:01 -0500, Chris Neff wrote:
> > > 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?
> > > >>
> > > >>
> > > >>
> > > >>
> > > >> _______________________________________________
> > > >> 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
> > > >
> > > >
> > > >
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> > 
> > 
> 
> 
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