ARROW-17362: [R] Implement dplyr::across() inside summarise()

r/R/dplyr-summarize.R

@@ -179,10 +179,10 @@ agg_funcs[["::"]] <- function(lhs, rhs) {
 
 # The following S3 methods are registered on load if dplyr is present
 
-summarise.arrow_dplyr_query <- function(.data, ...) {
+summarise.arrow_dplyr_query <- function(.data, ..., .groups = NULL) {
   call <- match.call()
   .data <- as_adq(.data)
-  exprs <- quos(...)
+  exprs <- expand_across(.data, quos(...))
   # Only retain the columns we need to do our aggregations
   vars_to_keep <- unique(c(
     unlist(lapply(exprs, all.vars)), # vars referenced in summarise
@@ -198,7 +198,7 @@ summarise.arrow_dplyr_query <- function(.data, ...) {
   .data <- dplyr::select(.data, intersect(vars_to_keep, names(.data)))
 
   # Try stuff, if successful return()
-  out <- try(do_arrow_summarize(.data, ...), silent = TRUE)
+  out <- try(do_arrow_summarize(.data, !!!exprs, .groups = .groups), silent = TRUE)
   if (inherits(out, "try-error")) {
     return(abandon_ship(call, .data, format(out)))
   } else {

r/tests/testthat/test-dplyr-summarize.R

@@ -1126,3 +1126,24 @@ test_that("We don't add unnecessary ProjectNodes when aggregating", {
     2
   )
 })
+
+test_that("Can use across() within summarise()", {
+  compare_dplyr_binding(
+    .input %>%
+      group_by(lgl) %>%
+      summarise(across(starts_with("dbl"), sum, .names = "sum_{.col}")) %>%
+      arrange(lgl) %>%
+      collect(),
+    example_data
+  )
+
+  # across() doesn't work in summarise when input expressions evaluate to bare field references
+  expect_warning(
+    example_data %>%
+      arrow_table() %>%
+      group_by(lgl) %>%
+      summarise(across(everything())) %>%
+      collect(),
+    regexp = "Expression int is not an aggregate expression or is not supported in Arrow; pulling data into R"
+  )
+})