Thanks a lot guys, I was sure that was possible > > The first list is for the syntax - (cols) := list(values)
Ok, I forgot this point 2015-06-25 15:53 GMT-04:00 Arunkumar Srinivasan <[email protected]>: > To add to Frank’s reply, I think `dt[, V3 := .(list(V1)), by=V2]` doesn’t > work with `1.9.4`, but has been fixed in 1.9.5. > The first list is for the syntax - (cols) := list(values). Cases like > `DT[, A := 1:5]` and is internally wrapped by `list()` for convenience, as > they are very common use cases. > -- > Arun > > On 25 Jun 2015 at 21:51:09, Frank Erickson ([email protected]) wrote: > > Oh, sorry, didn't notice you were making a new column, in that case: > dt[,V3:=list(list(V1)),by=V2] > > > On Thu, Jun 25, 2015 at 3:48 PM, Frank Erickson <[email protected]> > wrote: > >> 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 >>> >> >> > _______________________________________________ > datatable-help mailing list > [email protected] > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help > >
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