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Posted to issues@arrow.apache.org by "CaoZB (via GitHub)" <gi...@apache.org> on 2023/04/19 14:17:16 UTC
[GitHub] [arrow] CaoZB opened a new issue, #35236: params about FileReaderImpl::ReadRowGroups
CaoZB opened a new issue, #35236:
URL: https://github.com/apache/arrow/issues/35236
### Describe the usage question you have. Please include as many useful details as possible.
Interface `::arrow::Status ReadRowGroups` in file src/parquet/arrow/reader.h(https://github.com/apache/arrow/blob/main/cpp/src/parquet/arrow/reader.cc#L1219) has an input param named `const std::vector<int>& column_indices`, here are my questions:
1.I read the code and thought that column_indices should be leaf's column index, is that right? And If it is right, how can i get leaf's column index? I didn't find any interface about it.
2.line 1254 in file src/parquet/arrow/reader.cc(https://github.com/apache/arrow/blob/main/cpp/src/parquet/arrow/reader.cc#L1254),`RETURN_NOT_OK(ReadColumn(static_cast<int>(i), row_groups, reader.get(), &column));`, i think the first param `static_cast<int>(i)` should be index of `std::vector<SchemaField> schema_fields` in struct `SchemaManifest`(https://github.com/apache/arrow/blob/main/cpp/src/parquet/arrow/schema.h#L115), am i right? If so, i believe current passed value is not as expected.
### Component(s)
C++
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[GitHub] [arrow] mapleFU commented on issue #35236: [C++] params about FileReaderImpl::ReadRowGroups
Posted by "mapleFU (via GitHub)" <gi...@apache.org>.
mapleFU commented on issue #35236:
URL: https://github.com/apache/arrow/issues/35236#issuecomment-1515674378
You can also tag the issue with "parquet".
1. Yes. It's Leaf's column index. You can get the column from `SchemaManifest`
2. Not. If there is not nested struct, they should be near. But if we have nested struct, `schema_fields` would be a tree, and column is flatten.
You can talk a look at comment below:
```
/// To get the index for a particular leaf field, one can use
/// manifest().schema_fields to get the top level fields, and then walk the
/// tree to identify the relevant leaf fields and access its column_index.
/// To get the total number of leaf fields, use FileMetadata.num_columns().
```
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[GitHub] [arrow] mapleFU closed issue #35236: [C++][Parquet] params about FileReaderImpl::ReadRowGroups
Posted by "mapleFU (via GitHub)" <gi...@apache.org>.
mapleFU closed issue #35236: [C++][Parquet] params about FileReaderImpl::ReadRowGroups
URL: https://github.com/apache/arrow/issues/35236
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[GitHub] [arrow] mapleFU commented on issue #35236: [C++][Parquet] params about FileReaderImpl::ReadRowGroups
Posted by "mapleFU (via GitHub)" <gi...@apache.org>.
mapleFU commented on issue #35236:
URL: https://github.com/apache/arrow/issues/35236#issuecomment-1528824489
Does this solve your problem @CaoZB ?
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[GitHub] [arrow] CaoZB commented on issue #35236: [C++][Parquet] params about FileReaderImpl::ReadRowGroups
Posted by "CaoZB (via GitHub)" <gi...@apache.org>.
CaoZB commented on issue #35236:
URL: https://github.com/apache/arrow/issues/35236#issuecomment-1562195220
Yes, thank you so much.
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