使用mutate()和ifelse()

Question

很简单的问题。使用下面概述的第二种方法与方法1相比有什么缺点吗？或者它们实际上是相同的。(在处理变量的一些复杂条件时，我倾向于使用方法2，并且发现跟踪变量从一行到下一行更容易，但我担心这可能是糟糕的编码实践)

library(dplyr)

section <- c("MATH111", "MATH111", "ENG111")
grade <- c(78, 93, 56)
student <- c("David", "Kristina", "Mycroft")
gradebook <- data.frame(section, grade, student)
mutate(gradebook, Pass.Fail = ifelse(grade > 60, "Pass", "Fail"))

#approach 1
mutate(gradebook, letter = ifelse(grade %in% 60:69, "D",
                           ifelse(grade %in% 70:79, "C",
                           ifelse(grade %in% 80:89, "B",
                           ifelse(grade %in% 90:99, "A", "F")))))


#approach 2
gradebook$letter<-NA
gradebook <- gradebook %>% 
  mutate(letter=ifelse(grade < 60, "F",letter)) %>% 
  mutate(letter=ifelse(grade >60 & grade< 69, "D",letter)) %>% 
  mutate(letter=ifelse(grade >70 & grade< 79, "C",letter)) %>% 
  mutate(letter=ifelse(grade >80 & grade< 89, "B",letter)) %>% 
  mutate(letter=ifelse(grade >90 & grade< 99, "A",letter))
gradebook

Answer 1

似乎有一些错误，但如果您尝试使用dplyr::mutate，在本例中，dplyr::case_when将有所帮助。

gradebook %>%
  mutate(letter = case_when(
    grade < 60 ~ "F",
    grade < 70 ~ "D",
    grade < 80 ~ "C",
    grade < 90 ~ "B",
    grade < 100 ~ "A",
    T ~ NA_character_
    ))

  section grade  student letter
1 MATH111    78    David      C
2 MATH111    93 Kristina      A
3  ENG111    56  Mycroft      F