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 >
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