Dplyr管道groupby top_n未在组中获得top_n

I'm trying to obtain the top 2 names, sorted alphabetically, per group. I would think that top_n() would select this after I perform a group_by. However, this does not seem to be the case. This code shows the problem.

df <- data.frame(Group = c(0, 0, 0, 1, 1, 1),
                 Name = c("a", "c", "b", "e", "d", "f"))

df <- df %>%
      arrange(Name, Group) %>%
      group_by(Group) %>%
      top_n(2)

df

# A tibble: 2 x 2
# Groups:   Group [1]
  Group Name 
  <dbl> <chr>
1     1 e    
2     1 f 

预期输出为:

df <- df %>%
      arrange(Name, Group) %>%
      group_by(Group) %>%
      top_n(2)
df

      Group Name
1     0    a
2     0    b
3     1    d
4     1    e

或类似的东西。谢谢。