R 中等效的 Case 语句 [英] Case Statement Equivalent in R

问题描述

我在数据框中有一个变量，其中一个字段通常有 7-8 个值.我想在数据框中的新变量中将它们折叠 3 或 4 个新类别.最好的方法是什么?

I have a variable in a dataframe where one of the fields typically has 7-8 values. I want to collpase them 3 or 4 new categories within a new variable within the dataframe. What is the best approach?

如果我使用的是类似 SQL 的工具，但不确定如何在 R 中进行攻击，我会使用 CASE 语句.

I would use a CASE statement if I were in a SQL-like tool but not sure how to attack this in R.

您能提供的任何帮助将不胜感激！

Any help you can provide will be much appreciated!

推荐答案

case_when() 于 2016 年 5 月加入 dplyr，以类似于 memisc 的方式解决了这个问题::cases().

case_when(), which was added to dplyr in May 2016, solves this problem in a manner similar to memisc::cases().

例如:

library(dplyr)
mtcars %>% 
  mutate(category = case_when(
    .$cyl == 4 & .$disp < median(.$disp) ~ "4 cylinders, small displacement",
    .$cyl == 8 & .$disp > median(.$disp) ~ "8 cylinders, large displacement",
    TRUE ~ "other"
  )
)

从 dplyr 0.7.0 开始，

As of dplyr 0.7.0,

mtcars %>% 
  mutate(category = case_when(
    cyl == 4 & disp < median(disp) ~ "4 cylinders, small displacement",
    cyl == 8 & disp > median(disp) ~ "8 cylinders, large displacement",
    TRUE ~ "other"
  )
)

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