data.table 按索引粘贴选定的列

Question

我有一个如下的data.table

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)

我正在尝试将 DT 中的选定列 (selcol) 粘贴到一个新列中。

selcol = c("V3", "V4")

我知道DT[, "NEW" := paste0(V3, V4), with = FALSE] 可以解决问题。但我想在代码中使用selcol。

我已经尝试了以下

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]

如何使用data.table 做到这一点。

Answer 1

DT[, NEW := do.call(paste0, .SD), .SDcols = selcol] 
#    V1    V2    V3        V4     V5           NEW
#1: S01  Alan   Hal       Guy   John        HalGuy
#2: S02   Jay Barry     Wally   Bart    BarryWally
#3: S03 Bruce  Dick Jean-Paul Damien DickJean-Paul