I am a new user of the data.table package in R. I am trying to give a name to the new column created by a "group by" command
> DT = data.table(x=rep(c("a","b"),c(2,3)),y=1:5)
> DT
x y
1: a 1
2: a 2
3: b 3
4: b 4
5: b 5
> DT[,{z=sum(y);z+3},by=x]
x V1
1: a 6
2: b 15
- I would like to name the V1 (default) column directly (not having to use colnames), is it possible?
Additionally, is it possible to perform several group by operations in one command, that would result in something like:
x V1 V2 1: a 6 something 2: b 15 something
Thanks