Hi, I think you want
dt[,.(list(V1)),by=V2] # V2 V1 # 1: a 1,4 # 2: b 2,3 Using the .() notation makes it easier to keep track of what columns are being made, I find. --Frank On Thu, Jun 25, 2015 at 3:46 PM, Nicolas Paris <[email protected]> wrote: > 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 > > > > _______________________________________________ > datatable-help mailing list > [email protected] > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help >
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