This seems to work: DT <- data.table(obs=1:7, id=c(1,1,1,4,4,4,4), time=c(3,4,7,5,8,10,15)) DT[, value := 0] DT[!duplicated(id), value := 2] DT[!duplicated(id, fromLast = T), value := 1]
On 07/25/2014 08:29 PM, Frank S. wrote: > Hi all, I'm very novice in data.table management, and I have the > following doubt about this data: > > > >> DT <- data.table(obs=1:7, id=c(1,1,1,4,4,4,4), time=c(3,4,7,5,8,10,15)) >> DT > obs id time > 1: 1 1 3 > 2: 2 1 4 > 3: 3 1 7 > 4: 4 4 5 > 5: 5 4 8 > 6: 6 4 10 > 7: 7 4 15 > > > > In general, I know that I can select respectively the first and the last > observation within "id" group with: > > > > First observation: /DT[!duplicated(id)] / > > Last observation:/DT[!duplicated(id, fromLast=T)] / > > > > But, how can I add a new column, called "value", which contains all > zeros except: > > 1) The first observation within each "id" group, which is equal to 2 > > 2) The last observation within each "id" group, which is equal to 1 ? > > > > obs id time value > 1: 1 1 3 2 > 2: 2 1 4 0 > 3: 3 1 7 1 > 4: 4 4 5 2 > 5: 5 4 8 0 > 6: 6 4 10 0 > 7: 7 4 15 1 > > > > I've tried with conditionslas, ifelse, etc, but I get an error message. > Please, can you help me? > > > > Thanks in advance!! > > > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > 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
