R 使用 if else 逻辑为新列赋值

Question

我需要创建一个新列，该列基于在列中找到的三个可能值之一。

规则如下：

If it has c somewhere in it, the new column should be assigned "third"
If it has b, but not c somewhere in it, the new column should be assigned "second"
If it has a but not b or c somewhere in it, the new column should be assigned "first"

这是我的示例代码

x <- c('a,b,c', 'a', 'a,b')

myLetters <- data.frame(x)

setnames(myLetters, "theLetter") 

sapply(myLetters$, theLetter, function(x) 
if ('c' %in% myLetters$theLetter) {
    myLetters$letterStatus <- "third"
} else if ('b' %in% myLetters$theLetter) {
    myLetters$letterStatus <- "second" 
} else if ('a'  %in% myLetters$theLetter) {
    myLetters$letterStatus <- "first"
}
)

根据 myLetters$letterStatus 的示例数据，这是我想要的每一行的数据：

Row 1: third
Row 2: first
Row 3: second

目前我得到 "first" "first" "first" 但我不明白为什么。

你知道我如何解决这个问题以及为什么我每一行都排在第一位吗？

谢谢

Answer 1

使用矢量化（R 给我们的礼物）获得结果：

x <- c('a,b,c', 'a', 'a,b')
myLetters <- data.frame(x)
# myLetters
# x
# 1 a,b,c
# 2     a
# 3   a,b

myLetters$x1 = ifelse(grepl("c",myLetters$x), "third", ifelse(grepl("b",myLetters$x),"second", "first"))

R 使用 if else 逻辑为新列赋值

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