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

[Frank Erickson]

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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