[datatable-help] [data.table] Aggregate as vector

[Nicolas Paris]

Hi,

Here an example what I want to get :

> dt <- data.table(c(1,2,3,4),c("a","b","b","a"))
> dt
   V1 V2
1:  1  a
2:  2  b
3:  3  b
4:  4  a

What I want to get is a V3 column, containing an aggregated vector :
> dt
   V1 V2 V3
1:  1  a   c(1,4)
2:  2  b   c(2,3)

That does not work :

dt[,V3 := as.list(c(V1)),by=V2]

Is there a way to do so ?

Thanks
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