Adding a column with an if else statement - r

Question

I'm trying to cut numbers into categories to create a new column. Basically, trying to create a letter grade ("A", "B", "C", "D", "F") from scores.
I have reproduced a similar data frame to the one I'm having trouble with in the following code.
df <- tibble(score = rnorm(20:100, n = 150))
The code I wrote to add the grade column looks like this:
df_with_grade <- df %>%
mutate(Grade = if (score >= 90) {
"A"
} else if (score >= 80){
"B"
} else if (score >= 70){
"C"
} else if (score >= 60){
"D"
} else {
"F"
}
)
The code executes with a warning:
Warning messages:
1: In if (score >= 90) { :
the condition has length > 1 and only the first element will be used
2: In if (score >= 80) { :
the condition has length > 1 and only the first element will be used
3: In if (score >= 70) { :
the condition has length > 1 and only the first element will be used
4: In if (score >= 60) { :
the condition has length > 1 and only the first element will be used
The result is, all scores are assigned an "F"

Answer 1

How about
cut(df$score,breaks=c(0,6:10)*10,labels=rev(LETTERS[c(1:4,6)]))
? rev(LETTERS[c(1:4,6)]) might be too clever and doesn't save that many characters over c("F","D","C","B","A") ...

Answer 2

as suggested in the comments you can use case_when:
df_with_grade <- df %>%
mutate(Grade = case_when(score >= 90 ~ "A",
score >= 80 ~ "B",
score >= 70 ~ "C",
score >= 60 ~ "D",
TRUE ~ "F"))

Answer 3

You cannot use ifelse, it only works with binary conditions. Use cut like below,
df$Grade = cut(df$score,
breaks=c(0,60,70,80,90,100),
label=c("F","D","C","B","A"),
include.lowest =TRUE)

Answer 4

Just to show you can use ifelse.
df_with_grade <- df %>%
mutate(Grade =
ifelse(score>= 90, "A",
ifelse(score>=80, "B",
ifelse(score>=70, "C",
ifelse(score>=60, "D",
"F"))))
)