r - 链接 ifelse 语句的智能方法？

Question

当我必须链接 ifelse 语句时，它看起来像:

ifelse(input=="x","x1",
       ifelse(input=="y","x2",
              ifelse(input=="z","x3",NA)))

有没有更聪明的方法来做到这一点？我正在考虑创建表然后合并或类似的东西只是为了让代码看起来更好？

Answer 1

除了评论中的建议，您还可以使用 match通过以下方式。

创建示例数据:

set.seed(1)
vals_in <- c("x", "y", "z")   # unique values in your input vector
vec_in <- sample(vals_in, 10, replace = TRUE)  # sample from vals_in to create input
vals_out <-  c("x1", "x2", "x3")  # values to replace

现在，替换嵌套的 ifelse你可以这样做:

vec_out <- vals_out[match(vec_in, vals_in)]

结果是

vec_out
# [1] "x1" "x2" "x2" "x3" "x1" "x3" "x3" "x2" "x2" "x1"

两种方法的一些比较:

set.seed(1)
vals_in <- letters
vec_in <- sample(vals_in, 1e7, replace = TRUE)
vals_out <-  LETTERS

system.time(vals_out[match(vec_in, vals_in)])
       User      System verstrichen 
      0.378       0.020       0.398 
system.time(unname(setNames(vals_out, vals_in)[vec_in]))
       User      System verstrichen 
      1.020       0.062       1.084