[datatable-help] columns that show up when using both by-without-by and by=

[Arunkumar Srinivasan]

Me too, I dint at first get what the problem you were referring to, until I dint see `v1` in the output! :) 

Arun


On Friday, June 21, 2013 at 11:06 PM, Frank Erickson wrote:

> Ok. Thanks, Arun. I could've sworn it did that already, but seeing as it doesn't: yes, this is a feature request. :) --Frank
> 
> 
> On Fri, Jun 21, 2013 at 4:01 PM, Arunkumar Srinivasan <aragorn168b at gmail.com (mailto:aragorn168b at gmail.com)> wrote:
> > you can just do:
> > 
> > > DT[J(letters[4:6]), list(v1=v1, 1),by=v3]
> > 
> > If you use `by` only the columns in it will be included in the output. But it seems like what you request is a nicer feature and I am for it. Because, when you just do, DT[J(letters[4:6]), sum(v1)] it gives you "v1". But when using `by`, it disappears. I find with your suggestion this would be more consistent. 
> > 
> > 
> > Arun
> > 
> > 
> > On Friday, June 21, 2013 at 10:26 PM, Frank Erickson wrote:
> > 
> > 
> > > Hi,
> > > 
> > > I thought that when joining with J(x) and doing by=y, all the columns involved were put into .BY. However, I see that they are not: 
> > > 
> > > DT <- data.table(v1=letters[1:10],v2=1:10,v3=c(TRUE,FALSE),key="v1") 
> > > DT[J(letters[4:6]),1,by=v3]
> > > 
> > > I think I've just forgotten how to do this correctly (so that both v1 and v3 show up in the output). Any help would be appreciated. 
> > > 
> > > Thanks,
> > > 
> > > Frank 
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> > > 
> > > 
> > > 
> > > 
> > 
> > 
> > 
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