univert 0.4.0

Universal file converter (library and CLI)
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61

//! Apache Parquet → csv / json via the `parquet` crate's Arrow integration.

use std::fs;
use std::io::BufWriter;

use parquet::arrow::arrow_reader::ParquetRecordBatchReaderBuilder;

use crate::{Error, Job, Result};

pub fn parquet_to_csv(job: &Job) -> Result<()> {
  parquet_to_sv(job, b',')
}

pub fn parquet_to_tsv(job: &Job) -> Result<()> {
  parquet_to_sv(job, b'\t')
}

pub fn parquet_to_json(job: &Job) -> Result<()> {
  let reader = open_reader(job)?;
  let file = fs::File::create(job.output)?;
  let mut writer = arrow_json::ArrayWriter::new(BufWriter::new(file));
  for batch in reader {
    let batch =
      batch.map_err(|e| Error::other(format!("parquet read: {e}")))?;
    writer
      .write(&batch)
      .map_err(|e| Error::other(format!("json write: {e}")))?;
  }
  writer
    .finish()
    .map_err(|e| Error::other(format!("json finish: {e}")))?;
  Ok(())
}

fn parquet_to_sv(job: &Job, delimiter: u8) -> Result<()> {
  let reader = open_reader(job)?;
  let file = fs::File::create(job.output)?;
  let mut writer = arrow_csv::WriterBuilder::new()
    .with_header(true)
    .with_delimiter(delimiter)
    .build(BufWriter::new(file));
  for batch in reader {
    let batch =
      batch.map_err(|e| Error::other(format!("parquet read: {e}")))?;
    writer
      .write(&batch)
      .map_err(|e| Error::other(format!("csv write: {e}")))?;
  }
  Ok(())
}

fn open_reader(
  job: &Job,
) -> Result<parquet::arrow::arrow_reader::ParquetRecordBatchReader> {
  let file = fs::File::open(job.input)?;
  let builder = ParquetRecordBatchReaderBuilder::try_new(file)
    .map_err(|e| Error::other(format!("parquet open: {e}")))?;
  builder
    .build()
    .map_err(|e| Error::other(format!("parquet reader: {e}")))
}