在 R 中更改另一个 dataframe 上的单元格

Question

我想用另一个 dataframe 的值创建一个新列，如果 df1==1 中的单元格是当前的 df2 单元格

df1 <- c("1","2","3","4","5")
df2 <- c("a","b","c","d","e")

df <- cbind(df1,df2)
df
     df1 df2
[1,] "1" "a"
[2,] "2" "b"
[3,] "3" "c"
[4,] "4" "d"
[5,] "5" "e"

预期的答案是；

     df1 df2  my.column
[1,] "1" "a"     "a"
[2,] "2" "b"     "2"
[3,] "3" "c"     "3"
[4,] "4" "d"     "4"
[5,] "5" "e"     "5"

提前谢谢了

Answer 1

你可以使用ifelse ：

transform(df, my_col = ifelse(df1 == 1, df2, df1))

#  df1 df2 my_col
#1   1   a      a
#2   2   b      2
#3   3   c      3
#4   4   d      4
#5   5   e      5

等效于dplyr ：

library(dplyr)
df %>%mutate(my_col = ifelse(df1 == 1, df2, df1))

---

或者先复制df1值然后替换。

df$my_col <- df$df1
df$my_col[df$df1 == 1] <- df$df2[df$df1 == 1]

数据

df <- data.frame(df1,df2, stringsAsFactors = FALSE)

Answer 2

使用data.table将就地进行分配

library(data.table)
setDT(df)[, my_col := df1][df1 == 1, my_col := df2]
df
#   df1 df2 my_col
#1:   1   a      a
#2:   2   b      2
#3:   3   c      3
#4:   4   d      4
#5:   5   e      5

---

或与fifelse

setDT(df)[, my_col := fifelse(df1 == 1, df2, df1)]

或使用fcase

setDT(df)[, my_col := fcase(df1 == 1, df2, default = df1)]

数据

df <- data.frame(df1,df2, stringsAsFactors = FALSE)