巧妙地链接ifelse陈述？ [英] Smart way to chain ifelse statements?

问题描述

当我必须链接ifelse语句时，它看起来像：

When I have to chain ifelse statements, it looks like:

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

有更聪明的方法吗？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？

Is there a smarter way to do this? I'm thinking about creating tables then merging or something alike just to make the code look better?

推荐答案

除了建议之外评论你也可以用以下方式使用匹配。

Apart from the suggestions in comments you could also use match in the following way.

创建样本数据：

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，要替换嵌套的 ifelse s你可以这样做：

Now, to replace the nested ifelses you could do:

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"

---

两种方法的比较：

---

A little comparison of two approaches:

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 

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