(arrow) branch main updated: GH-40742: [R] fix max_rows_per_group must be a positive number (#49709)

[thisisnic]

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thisisnic pushed a commit to branch main
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The following commit(s) were added to refs/heads/main by this push:
     new 9a0afd9e95 GH-40742: [R] fix max_rows_per_group must be a positive 
number (#49709)
9a0afd9e95 is described below

commit 9a0afd9e9545444b492237cc9db7eb4549ce09f5
Author: Nic Crane <thisis...@gmail.com>
AuthorDate: Tue May 5 10:24:54 2026 -0400

    GH-40742: [R] fix max_rows_per_group must be a positive number (#49709)
    
    ### Rationale for this change
    
    Error message due to faulty checking
    
    ### What changes are included in this PR?
    
    Change checking circumstances
    
    ### Are these changes tested?
    
    Yes
    
    ### Are there any user-facing changes?
    
    No
    
    ### AI usage
    
    Used Claude to generate this - will double check before marking ready for 
review
    * GitHub Issue: #40742
    
    Authored-by: Nic Crane <thisis...@gmail.com>
    Signed-off-by: Nic Crane <thisis...@gmail.com>
---
 r/R/dataset-write.R                   | 28 ++++++++++++++++++++++++----
 r/tests/testthat/test-dataset-write.R | 10 ++++++++++
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/r/R/dataset-write.R b/r/R/dataset-write.R
index 663e1b8f08..dd675b40d0 100644
--- a/r/R/dataset-write.R
+++ b/r/R/dataset-write.R
@@ -218,7 +218,12 @@ write_dataset <- function(
   existing_data_behavior_opts <- c("delete_matching", "overwrite", "error")
   existing_data_behavior <- match(match.arg(existing_data_behavior), 
existing_data_behavior_opts) - 1L
 
-  if (!missing(max_rows_per_file) && missing(max_rows_per_group) && 
max_rows_per_group > max_rows_per_file) {
+  if (
+    !missing(max_rows_per_file) &&
+      missing(max_rows_per_group) &&
+      max_rows_per_file > 0 &&
+      max_rows_per_group > max_rows_per_file
+  ) {
     max_rows_per_group <- max_rows_per_file
   }
 
@@ -290,7 +295,12 @@ write_delim_dataset <- function(
   quote = c("needed", "all", "none"),
   preserve_order = FALSE
 ) {
-  if (!missing(max_rows_per_file) && missing(max_rows_per_group) && 
max_rows_per_group > max_rows_per_file) {
+  if (
+    !missing(max_rows_per_file) &&
+      missing(max_rows_per_group) &&
+      max_rows_per_file > 0 &&
+      max_rows_per_group > max_rows_per_file
+  ) {
     max_rows_per_group <- max_rows_per_file
   }
 
@@ -343,7 +353,12 @@ write_csv_dataset <- function(
   quote = c("needed", "all", "none"),
   preserve_order = FALSE
 ) {
-  if (!missing(max_rows_per_file) && missing(max_rows_per_group) && 
max_rows_per_group > max_rows_per_file) {
+  if (
+    !missing(max_rows_per_file) &&
+      missing(max_rows_per_group) &&
+      max_rows_per_file > 0 &&
+      max_rows_per_group > max_rows_per_file
+  ) {
     max_rows_per_group <- max_rows_per_file
   }
 
@@ -395,7 +410,12 @@ write_tsv_dataset <- function(
   quote = c("needed", "all", "none"),
   preserve_order = FALSE
 ) {
-  if (!missing(max_rows_per_file) && missing(max_rows_per_group) && 
max_rows_per_group > max_rows_per_file) {
+  if (
+    !missing(max_rows_per_file) &&
+      missing(max_rows_per_group) &&
+      max_rows_per_file > 0 &&
+      max_rows_per_group > max_rows_per_file
+  ) {
     max_rows_per_group <- max_rows_per_file
   }
 
diff --git a/r/tests/testthat/test-dataset-write.R 
b/r/tests/testthat/test-dataset-write.R
index d62b888163..8fed358dc3 100644
--- a/r/tests/testthat/test-dataset-write.R
+++ b/r/tests/testthat/test-dataset-write.R
@@ -576,6 +576,16 @@ test_that("max_rows_per_group is adjusted if at odds with 
max_rows_per_file", {
   )
 })
 
+test_that("max_rows_per_file = 0 does not trigger max_rows_per_group 
adjustment (ARROW-40742)", {
+  skip_if_not_available("parquet")
+
+  # max_rows_per_file = 0 means "no limit" and should not error
+  dst_dir <- make_temp_dir()
+  expect_no_error(
+    write_dataset(df1, dst_dir, max_rows_per_file = 0L)
+  )
+})
+
 
 test_that("write_dataset checks for format-specific arguments", {
   df <- tibble::tibble(