I have a data table as follows
DT <- structure(list(V1 = structure(1:3, .Label = c("S01", "S02", "S03"), class = "factor"), V2 = structure(c(1L, 3L, 2L), .Label = c("Alan", "Bruce", "Jay"), class = "factor"), V3 = structure(c(3L, 1L, 2L), .Label = c("Barry", "Dick", "Hal"), class = "factor"), V4 = structure(c(1L, 3L, 2L), .Label = c("Guy", "Jean-Paul", "Wally"), class = "factor"), V5 = structure(c(3L, 1L, 2L), .Label = c("Bart", "Damien", "John"), class = "factor")), .Names = c("V1", "V2", "V3", "V4", "V5"), class = "data.frame", row.names = c(NA, -3L)) setDT(DT) setkey(DT, V1)
I am trying to insert together selected columns ( selcol ) in a DT in a new column.
selcol = c("V3", "V4")
I know that DT[, "NEW" := paste0(V3, V4), with = FALSE] does the trick. But I would like to use selcol in code.
I tried the following
DT[, "NEW" := paste0(which(colnames(DT) %in% selcol)), with = TRUE] DT[, "NEW" := paste0(which(colnames(DT) %in% selcol)), with = TRUE] DT[, "NEW" := paste0(3, 4), with = TRUE] DT[, "NEW" := paste(3, 4), with = TRUE]
How to do this with data.table .