如何根据 R 中的条件创建新变量 [英] How can I create a new variable based on conditions in R

问题描述

我正在尝试根据某些条件创建一个新变量.

I am trying to create a new variable based on some conditions.

我的数据看起来像

a   b
1   NA
2   3
3   3
NA  2
NA  NA

我想要的是一个变量 c 使得

What I want is a variable c such that

• 当a不是NA时，b是NA，c = a

当a是NA时，b不是NA，c = b

当a为NA时，b为NA，c = NA

当 a 不是 NA 时，b 不是 NA，并且 a== b, c = a

when a is not NA, b is not NA, and a == b, c = a

当 a 不是 NA 时，b 不是 NA，并且 a!= b, c = "multiple_values"

when a is not NA, b is not NA, and a != b, c = "multiple_values"

我该怎么做?

似乎 ifelse() 不能做我想做的事.

It seems like ifelse() can't do what I want.

推荐答案

除了条件之一，即'a'、'b'中的非NA元素，且彼此不相等，所有其他coalesce 满足条件.因此，我们可以通过应用 coalesce

Except for one of the condition, i.e non-NA elements in both 'a', 'b', and they are not equal to each others, all other conditions are met with coalesce. So, we can do a case_when to generate the "multiple_values" based on the last condition and all others by applying coalesce

library(dplyr)
df1 %>%
     mutate(c = case_when(!is.na(a) & !is.na(b) & a != b ~ "multiple_values", 
               TRUE ~ as.character(coalesce(a, b))))
#   a  b               c
#1  1 NA               1
#2  2  3 multiple_values
#3  3  3               3
#4 NA  2               2
#5 NA NA            <NA>

数据

df1 <- structure(list(a = c(1L, 2L, 3L, NA, NA), b = c(NA, 3L, 3L, 2L, 
 NA)), class = "data.frame", row.names = c(NA, -5L))

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