[R] Allow multiple arguments to n_distinct()

[asfimport]

ARROW-13620 and ARROW-14036 added support for the n_distinct() function in the dplyr verb summarise() but only with a single argument. Add support for multiple arguments to n_distinct(). This should return the number of unique combinations of values in the specified columns/expressions.

See the comment about this here: #11257 (comment)

Reporter: Ian Cook / @ianmcook

_{Note: This issue was originally created as ARROW-14209. Please see the migration documentation for further details.}

[asfimport]

Dewey Dunnington / @paleolimbot:
Where n_distinct() binding is:

arrow/r/R/dplyr-functions.R

Lines 1091 to 1097 in 6e20c6b

	agg_funcs$n_distinct <- function(..., na.rm = FALSE) {
	list(
	fun = "count_distinct",
	data = ensure_one_arg(list2(...), "n_distinct"),
	options = list(na.rm = na.rm)
	)
	}

Reprex:

library(arrow, warn.conflicts = FALSE)
library(dplyr, warn.conflicts = FALSE)

record_batch(
  a = c(1, 1, 2, 2, 1, NA, NA),
  b = c("a", "b", "c", "c", "a", "b", NA)
) %>% 
  summarise(
    distinct_vals_with_na = n_distinct(a, b, na.rm = FALSE),
    distinct_vals = n_distinct(a, b, na.rm = TRUE)
  )
#> Warning: Error : In n_distinct(a, b, na.rm = FALSE), Multiple arguments to
#> n_distinct() not supported in Arrow; pulling data into R
#> # A tibble: 1 × 2
#>   distinct_vals_with_na distinct_vals
#>                   <int>         <int>
#> 1                     5             3

[asfimport]

Todd Farmer / @toddfarmer:
This issue was last updated over 90 days ago, which may be an indication it is no longer being actively worked. To better reflect the current state, the issue is being unassigned per project policy. Please feel free to re-take assignment of the issue if it is being actively worked, or if you plan to start that work soon.

[github-actions]

This issue has been marked as stale because it has had no activity in the past 365 days. Please remove the stale label or comment below, or this issue will be closed in 14 days. If this improvement is still desired but has no current owner, please add the 'Status: needs champion' label.