[GitHub] [arrow] jorisvandenbossche commented on a change in pull request #8301: ARROW-10100: [C++][Python][Dataset] Add ParquetFileFragment::Subset method

[GitBox <gi...@apache.org>]

jorisvandenbossche commented on a change in pull request #8301:
URL: https://github.com/apache/arrow/pull/8301#discussion_r496842872



##########
File path: cpp/src/arrow/dataset/file_parquet.cc
##########
@@ -575,6 +575,39 @@ Result<FragmentVector> ParquetFileFragment::SplitByRowGroup(
   return fragments;
 }
 
+Result<std::shared_ptr<Fragment>> ParquetFileFragment::Subset(
+    const std::shared_ptr<Expression>& predicate) {
+  RETURN_NOT_OK(EnsureCompleteMetadata());
+  ARROW_ASSIGN_OR_RAISE(auto row_groups, FilterRowGroups(*predicate));
+
+  ARROW_ASSIGN_OR_RAISE(auto new_fragment,
+                        parquet_format_.MakeFragment(source_, partition_expression(),
+                                                     row_groups, physical_schema_));
+  return new_fragment;
+}
+
+Result<std::shared_ptr<Fragment>> ParquetFileFragment::Subset(
+    const std::vector<int> row_group_ids) {
+  std::vector<RowGroupInfo> row_groups;
+

Review comment:
       Here I would still need to check that all row_group_ids exist in the fragment




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