[I] Documentation fix: example in parquet/src/column/mod.rs is incorrect [arrow-rs]

["zgershkoff (via GitHub)" <gi...@apache.org>]

zgershkoff opened a new issue, #5560:
URL: https://github.com/apache/arrow-rs/issues/5560

   **Describe the bug**
   <!--
   A clear and concise description of what the bug is.
   -->
   If I try to compile and run the example given in the documentation for `parquet::column`, the assertions at the end fail.
   
   **To Reproduce**
   <!--
   Steps to reproduce the behavior:
   -->
   `cargo build` with the following in `main.rs`:
   
   ```rust
   use std::fs;
   use parquet::column::reader::ColumnReader;
   use parquet::file::reader::FileReader;
   use parquet::file::serialized_reader::SerializedFileReader;
   use parquet::data_type::Int32Type;
   use parquet::file::writer::SerializedFileWriter;
   use std::sync::Arc;
   use std::path::Path;
   use parquet::schema::parser::parse_message_type;
   
   
   fn main() {
       let path = Path::new("column_sample.parquet");
   
       // Writing data using column writer API.
   
       let message_type = "
         message schema {
           optional group values (LIST) {
             repeated group list {
               optional INT32 element;
             }
           }
         }
       ";
       let schema = Arc::new(parse_message_type(message_type).unwrap());
       let file = fs::File::create(path).unwrap();
       let mut writer = SerializedFileWriter::new(file, schema, Default::default()).unwrap();
   
       let mut row_group_writer = writer.next_row_group().unwrap();
       while let Some(mut col_writer) = row_group_writer.next_column().unwrap() {
           col_writer
               .typed::<Int32Type>()
               .write_batch(&[1, 2, 3], Some(&[3, 3, 3, 2, 2]), Some(&[0, 1, 0, 1, 1]))
               .unwrap();
           col_writer.close().unwrap();
       }
       row_group_writer.close().unwrap();
   
       writer.close().unwrap();
   
       // Reading data using column reader API.
   
       let file = fs::File::open(path).unwrap();
       let reader = SerializedFileReader::new(file).unwrap();
       let metadata = reader.metadata();
   
       let mut values = vec![0; 8];
       let mut def_levels = vec![0; 8];
       let mut rep_levels = vec![0; 8];
   
       for i in 0..metadata.num_row_groups() {
           let row_group_reader = reader.get_row_group(i).unwrap();
           let row_group_metadata = metadata.row_group(i);
   
           for j in 0..row_group_metadata.num_columns() {
               let mut column_reader = row_group_reader.get_column_reader(j).unwrap();
               match column_reader {
                   // You can also use `get_typed_column_reader` method to extract typed reader.
                   ColumnReader::Int32ColumnReader(ref mut typed_reader) => {
                       let (records, values, levels) = typed_reader.read_records(
                           8, // maximum records to read
                           Some(&mut def_levels),
                           Some(&mut rep_levels),
                           &mut values,
                       ).unwrap();
                       assert_eq!(records, 2);
                       assert_eq!(levels, 5);
                       assert_eq!(values, 3);
                   }
                   _ => {}
               }
           }
       }
   
       assert_eq!(values, vec![1, 2, 3, 0, 0, 0, 0, 0]);
       assert_eq!(def_levels, vec![3, 3, 3, 2, 2, 0, 0, 0]);
       assert_eq!(rep_levels, vec![0, 1, 0, 1, 1, 0, 0, 0]);
   }
   
   ```
   
   **Expected behavior**
   <!--
   A clear and concise description of what you expected to happen.
   -->
   The assertions should be correct. I'm surprised that the examples in the documentation don't compile and run as part of the test suite.
   
   **Additional context**
   <!--
   Add any other context about the problem here.
   -->
   This line https://github.com/apache/arrow-rs/blob/master/parquet/src/column/reader/decoder.rs#L236 appears to be the culprit, in that it resizes the `values` vector, and then only passes the new part of the vector to `self.decoder.as_mut().unwrap().read()`. This was changed 3 months ago as part of #5177.


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Re: [I] Documentation fix: example in parquet/src/column/mod.rs is incorrect [arrow-rs]

["tustvold (via GitHub)" <gi...@apache.org>]

tustvold commented on issue #5560:
URL: https://github.com/apache/arrow-rs/issues/5560#issuecomment-2061309312

   `label_issue.py` automatically added labels {'parquet'} from #5561


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Re: [I] Documentation fix: example in parquet/src/column/mod.rs is incorrect [arrow-rs]

["tustvold (via GitHub)" <gi...@apache.org>]

tustvold closed issue #5560: Documentation fix: example in parquet/src/column/mod.rs is incorrect
URL: https://github.com/apache/arrow-rs/issues/5560


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