我的问题涉及创建一个变量,该变量依赖于data.table中的其他列,当事先没有知道任何变量名时.
下面是一个玩具示例,其中我有5行,当条件等于A时,新变量应为1,否则为4.
library(data.table)
DT <- data.table(Con = c("A","A","B","A","B"),
Eval_A = rep(1,5),
Eval_B = rep(4,5))
Col1 <- "Con"
Col2 <- "Eval_A"
Col3 <- "Eval_B"
Col4 <- "Ans"
下面的代码有效,但感觉我误用了包!
DT[,Col4:=ifelse(DT[[Col1]]=="A",
DT[[Col2]],
DT[[Col3]]),with=FALSE]
更新: 谢谢,我快速完成了以下答案.一旦在data.table上有500万行而只有相关列,并在添加10个非相关列后再次出现,下面是结果:
+-------------------------+---------------------+------------------+
| Method | Only relevant cols. | With extra cols. |
+-------------------------+---------------------+------------------+
| List method | 1.8 | 1.91 |
| Grothendieck - get/if | 26.79 | 30.04 |
| Grothendieck - get/join | 0.48 | 1.56 |
| Grothendieck - .SDCols | 0.38 | 0.79 | …