Is this intended? If we use j = list(x = "X", y = numeric(0)) we get a row but if we use just list(y = numeric(0)) then we do not get a row. In the first case it filled in the zero length component with NA and in the second case it just omitted the row entirely:
> dd <- data.table(a = 1:3) > dd a 1: 1 2: 2 3: 3 > dd[, list(x = "X", y = numeric(0)), by = a] a x y 1: 1 X NA 2: 2 X NA 3: 3 X NA > dd[, list(y = numeric(0)), by = a] Empty data.table (0 rows) of 2 cols: a,y -- Statistics & Software Consulting GKX Group, GKX Associates Inc. tel: 1-877-GKX-GROUP email: ggrothendieck at gmail.com _______________________________________________ datatable-help mailing list [email protected] https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
