Module parquet::arrow

Provides API for reading/writing Arrow RecordBatches and Arrays to/from Parquet Files.

Apache Arrow is a cross-language development platform for in-memory data.

Example of writing Arrow record batch to Parquet file

 use arrow::array::{Int32Array, ArrayRef};
 use arrow::record_batch::RecordBatch;
 use parquet::arrow::arrow_writer::ArrowWriter;
 use parquet::file::properties::WriterProperties;
 use std::fs::File;
 use std::sync::Arc;
 let ids = Int32Array::from(vec![1, 2, 3, 4]);
 let vals = Int32Array::from(vec![5, 6, 7, 8]);
 let batch = RecordBatch::try_from_iter(vec![
   ("id", Arc::new(ids) as ArrayRef),
   ("val", Arc::new(vals) as ArrayRef),
 ]).unwrap();

 let file = File::create("data.parquet").unwrap();

 // Default writer properties
 let props = WriterProperties::builder().build();

 let mut writer = ArrowWriter::try_new(file, batch.schema(), Some(props)).unwrap();

 writer.write(&batch).expect("Writing batch");

 // writer must be closed to write footer
 writer.close().unwrap();

WriterProperties can be used to set Parquet file options

use parquet::file::properties::WriterProperties;
use parquet::basic::{ Compression, Encoding };
use parquet::file::properties::WriterVersion;

// File compression
let props = WriterProperties::builder()
    .set_compression(Compression::SNAPPY)
    .build();

Example of reading parquet file into arrow record batch

use arrow::record_batch::RecordBatchReader;
use parquet::file::reader::SerializedFileReader;
use parquet::arrow::{ParquetFileArrowReader, ArrowReader};
use std::sync::Arc;
use std::fs::File;


let file = File::open("data.parquet").unwrap();
let file_reader = SerializedFileReader::new(file).unwrap();
let mut arrow_reader = ParquetFileArrowReader::new(Arc::new(file_reader));

println!("Converted arrow schema is: {}", arrow_reader.get_schema().unwrap());
println!("Arrow schema after projection is: {}",
   arrow_reader.get_schema_by_columns(vec![0], true).unwrap());

let mut record_batch_reader = arrow_reader.get_record_reader(2048).unwrap();

for maybe_record_batch in record_batch_reader {
   let record_batch = maybe_record_batch.unwrap();
   if record_batch.num_rows() > 0 {
       println!("Read {} records.", record_batch.num_rows());
   } else {
       println!("End of file!");
   }
}

Re-exports

pub use self::arrow_reader::ArrowReader;

pub use self::arrow_reader::ParquetFileArrowReader;

pub use self::arrow_writer::ArrowWriter;

Modules

arrow_reader

Contains reader which reads parquet data into arrow array.

arrow_writer

Contains writer which writes arrow data into parquet data.

Constants

ARROW_SCHEMA_META_KEY

Schema metadata key used to store serialized Arrow IPC schema

Functions

arrow_to_parquet_schema

Convert arrow schema to parquet schema

parquet_to_arrow_schema

Convert Parquet schema to Arrow schema including optional metadata. Attempts to decode any existing Arrow schema metadata, falling back to converting the Parquet schema column-wise

parquet_to_arrow_schema_by_columns

Convert parquet schema to arrow schema including optional metadata, only preserving some leaf columns.

parquet_to_arrow_schema_by_root_columns

Convert parquet schema to arrow schema including optional metadata, only preserving some root columns. This is useful if we have columns a.b, a.c.e and a.d, and want a with all its child fields