You almost had it right with number 2: DT[,value:=ifelse(!duplicated(id),0,2)]
On Tue, Aug 25, 2015 at 12:26 PM Eduard Antonyan <[email protected]> wrote: > DT[, value := c(2, rep(0, .N-1)), by = id] > > On Tue, Aug 25, 2015 at 11:17 AM, Frank S. <[email protected]> wrote: > >> Hello everyone, >> I ask a question directly linked with other question which I was answered >> in this list a year ago. Let the data table be: >> DT <- data.table(obs=1:7, id=c(1,1,1,4,4,4,4), time=c(3,4,7,5,8,10,15)) >> >> Now I add a new column, called "value", which contains all zeros except >> the first observation within each "id" group, which is equal to 2. >> One possible solution I was given is the following two code lines: >> > DT[ , value:=0] >> > DT[!duplicated(id), value:=2] >> >> But I wonder if it is possible to do the same ON A SINGLE CODE LINE. I >> have tried different options but they doesn't work: >> 1) DT[ , value:= c(0, 2), by=id] >> 2) DT[ , value:= ifelse( DT[!duplicated(id)]==T, 2, 0), by=id] >> >> Many 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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