Counting and completing, with special behaviour for `grouped_df`

complete_count.R

library(tidyverse)
library(rlang)

complete_count <- function(.data, ...) {
  UseMethod("complete_count")
}

complete_count.grouped_df <- function(.data, ...) {
  grps <- groups(.data)
  
  .data %>% 
    ungroup() %>% 
    complete_count(!!!grps, ...) %>%
    group_by(!!!grps)
}

complete_count.data.frame <- function(.data, ...) {
  dots <- enquos(...)
  
  .data %>%
    count(!!!dots) %>%
    complete(!!!dots, fill = list(n = 0L))
}

df <- tibble(a = c(1, 1, 2), b = c(3, 4, 5))

# Normally `complete` will just complete within groups
df %>% 
  group_by(a) %>% 
  count(b) %>% 
  complete(b)
#> # A tibble: 3 x 3
#> # Groups:   a [2]
#>       a     b     n
#>   <dbl> <dbl> <int>
#> 1  1.00  3.00     1
#> 2  1.00  4.00     1
#> 3  2.00  5.00     1

# `complete_count` will complete across groups, too
df %>% 
  group_by(a) %>% 
  complete_count(b)
#> # A tibble: 6 x 3
#> # Groups:   a [2]
#>       a     b     n
#>   <dbl> <dbl> <int>
#> 1  1.00  3.00     1
#> 2  1.00  4.00     1
#> 3  1.00  5.00     0
#> 4  2.00  3.00     0
#> 5  2.00  4.00     0
#> 6  2.00  5.00     1