如何使用特定的函数和条件在dataframe中改变新的列？Tidyverse/R

library(tidyverse)

df <- tibble(
  name = c("Alice", "Bob", "Charlie", "David"),
  age = c(20, 21, 22, 23),
  score = c(80, 85, 90, 95)
)

df <- df %>% 
  mutate(grade = case_when(
    score >= 90 ~ "优秀",
    score >= 80 ~ "良好",
    score >= 70 ~ "中等",
    TRUE ~ "不及格"
  ))

print(df)

# A tibble: 4 x 4
  name    age score grade 
  <chr> <dbl> <dbl> <chr>
1 Alice    20    80 良好 
2 Bob      21    85 良好 
3 Charlie  22    90 优秀 
4 David    23    95 优秀