mapleFU commented on code in PR #39337:
URL: https://github.com/apache/arrow/pull/39337#discussion_r1434666050
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cpp/src/parquet/metadata.cc:
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@@ -793,26 +793,19 @@ class FileMetaData::FileMetaDataImpl {
std::shared_ptr<FileMetaData> out(new FileMetaData());
out->impl_ = std::make_unique<FileMetaDataImpl>();
- out->impl_->metadata_ = std::make_unique<format::FileMetaData>();
+ out->impl_->metadata_ = std::make_unique<format::FileMetaData>(*metadata_);
+ auto output_metadata = out->impl_->metadata_.get();
- auto metadata = out->impl_->metadata_.get();
- metadata->version = metadata_->version;
- metadata->schema = metadata_->schema;
-
- metadata->row_groups.resize(row_groups.size());
+ // Discard row groups that are not in the subset
+ output_metadata->num_rows = 0;
+ output_metadata->row_groups.clear();
Review Comment:
Note:
Here will introduce a more round for copying `metadata_->row_groups`.
Should I:
```
bool isset_rowgroup = metadata->isset.row_groups;
metadata->isset.row_groups = false;
auto row_groups = std::move(metadata->row_groups);
// Copying thrift
// ...
// Assign row_groups back
metadata->row_groups = std::move(row_groups);
metadata->isset.row_groups = ...
// .. Handle RowGroups
```
? cc @wgtmac @pitrou
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