聪明的方式链ifelse语句？

Question

当我不得不链ifelse语句，它看起来像：

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

有没有一种更聪明的办法做到这一点？我正在考虑创建表格然后合并或者只是为了使代码看起来更好？

Answer 1

从建议

除了在注释中，你也可以通过以下方式使用match。

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，替换的嵌套ifelse是你可以做：

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" 

---

一点比较两种方法：

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 

Answer 2

你可以尝试这样的函数之一：

choice <- function(input) { 
    switch(input, 
     "x"="x1", 
     "y"="x2", 
     "z"="x3", 
     NA) 
} 
#> choice("x") 
#[1] "x1" 
#> choice("z") 
#[1] "x3" 
#> choice("other") 
#[1] NA 

Answer 3

另一种办法是使用setNames

unname(setNames(vals_out, vals_in)[vec_in]) 
#[1] "x1" "x2" "x2" "x3" "x1" "x3" "x3" "x2" "x2" "x1" 

注：摘自@docendo discimus后的例子。