[R] count should return an ungrouped dataframe

[asfimport]

Unless grouped before dplyr::count returns a ungrouped data.frame. The arrow implement preserves the grouping variables:

 

library(arrow, warn.conflicts = FALSE)
library(dplyr, warn.conflicts = FALSE)
tf1 <- tempfile()
dir.create(tf1)
starwars |>
  write_dataset(tf1)

# no group ----------------------------------------------------------------
## dplyr behaviour
count_dplyr_no_group <- starwars %>%
  count(gender, homeworld, species)
group_vars(count_dplyr_no_group)
#> character(0)
## arrow behaviour
count_arrow_no_group <- open_dataset(tf1) %>%
  count(gender, homeworld, species) %>%
  collect()
group_vars(count_arrow_no_group)
#> [1] "gender"    "homeworld"

If I am correct that this is a undesired behaviour I think it can be fixed here using this patch:

 

count.arrow_dplyr_query <- function(x, ..., wt = NULL, sort = FALSE, name = NULL) {
  if (!missing(...)) {
    out <- dplyr::group_by(x, ..., .add = TRUE)
  } else {
    out <- x
  }
  out <- dplyr::tally(out, wt = {{ wt }}, sort = sort, name = name)

  gv <- dplyr::group_vars(x)
  if (rlang::is_empty(gv)) {
    out <- dplyr::ungroup(out)
  } else {
    # Restore original group vars
    out$group_by_vars <- gv
  }
  out
}

 

I can submit a PR with some tests if that would be helpful.

Reporter: Sam Albers / @boshek
Assignee: Sam Albers / @boshek

PRs and other links:

• GitHub Pull Request #12435

_{Note: This issue was originally created as ARROW-15679. Please see the migration documentation for further details.}

[asfimport]

Nicola Crane / @thisisnic:
Hi @boshek - thanks for reporting this!  A PR with some tests sounds great - please do, and let me know if there's anything you're not sure of, or that I can help with.

[asfimport]

Ian Cook / @ianmcook:
Issue resolved by pull request 12435
#12435