what is the function to sum specific rows in data frame in R?

Question

I want to sum specific rows by my choice. my data is like this :

df_new <- data.frame(country = c('US', 'US','US', 'UK','UK','UK'),
                 team = c('A', 'B','C','A','F', 'E'),
                 x1990 = c(11, 8,2,16,1,21),
                 x2005 = c(6, 4,2,10,1, 14))

and I want to prepare it like this:

df_sum <- data.frame(country = c('US','US', 'UK','UK'),
                 team = c('A', 'B','A','F'),
                 x1990 = c(11, 10,16,22),
                 x2005 = c(6, 6,10, 15))

Answer 1

You may try

df_new%>%
  mutate(team = case_when(
    team %in% c("B", "C") ~ "B",
    team %in% c("E", "F") ~ "F",
    T ~ team
  )) %>%
  group_by(country, team) %>%
  summarise(across(is.numeric, ~sum(.x))) %>%
  arrange(desc(country))

  country team  x1990 x2005
  <chr>   <chr> <dbl> <dbl>
1 US      A        11     6
2 US      B        10     6
3 UK      A        16    10
4 UK      F        22    15

You may need to specify your some inside case_when part.