是否有按国家和年份汇总单个级别数据的R函数？

library(dplyr)

df <- data.frame(
  country = c("China", "China", "USA", "USA", "USA"),
  year = c(2019, 2020, 2019, 2020, 2021),
  value = c(100, 200, 150, 250, 300)
)

grouped_df <- df %>% 
  group_by(country, year)

summarized_df <- grouped_df %>% 
  summarize(total_value = sum(value))

print(summarized_df)

# A tibble: 3 x 3
# Groups:   country [2]
  country  year total_value
  <chr>   <dbl>       <dbl>
1 China    2019         100
2 China    2020         200
3 USA      2019         150
4 USA      2020         250
5 USA      2021         300