polars-io 0.26.1

IO related logic for the Polars DataFrame library
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
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130

use std::io::{Read, Seek};

use arrow::io::avro::{self, read};
use polars_core::prelude::*;

use super::{finish_reader, ArrowChunk, ArrowReader, ArrowResult};
use crate::avro::convert_err;
use crate::prelude::*;

/// Read Apache Avro format into a DataFrame
///
/// # Example
/// ```
/// use std::fs::File;
/// use polars_core::prelude::*;
/// use polars_io::avro::AvroReader;
/// use polars_io::SerReader;
///
/// fn example() -> PolarsResult<DataFrame> {
///     let file = File::open("file.avro").expect("file not found");
///
///     AvroReader::new(file)
///             .finish()
/// }
/// ```
#[must_use]
pub struct AvroReader<R> {
    reader: R,
    rechunk: bool,
    n_rows: Option<usize>,
    columns: Option<Vec<String>>,
    projection: Option<Vec<usize>>,
}

impl<R: Read + Seek> AvroReader<R> {
    /// Get schema of the Avro File
    pub fn schema(&mut self) -> PolarsResult<Schema> {
        let schema = self.arrow_schema()?;
        Ok((schema.fields.iter()).into())
    }

    /// Get arrow schema of the avro File, this is faster than a polars schema.
    pub fn arrow_schema(&mut self) -> PolarsResult<ArrowSchema> {
        let metadata =
            avro::avro_schema::read::read_metadata(&mut self.reader).map_err(convert_err)?;
        let schema = read::infer_schema(&metadata.record)?;
        Ok(schema)
    }

    /// Stop reading when `n` rows are read.
    pub fn with_n_rows(mut self, num_rows: Option<usize>) -> Self {
        self.n_rows = num_rows;
        self
    }

    /// Set the reader's column projection. This counts from 0, meaning that
    /// `vec![0, 4]` would select the 1st and 5th column.
    pub fn with_projection(mut self, projection: Option<Vec<usize>>) -> Self {
        self.projection = projection;
        self
    }

    /// Columns to select/ project
    pub fn with_columns(mut self, columns: Option<Vec<String>>) -> Self {
        self.columns = columns;
        self
    }
}

impl<R> ArrowReader for read::Reader<R>
where
    R: Read + Seek,
{
    fn next_record_batch(&mut self) -> ArrowResult<Option<ArrowChunk>> {
        self.next().map_or(Ok(None), |v| v.map(Some))
    }
}

impl<R> SerReader<R> for AvroReader<R>
where
    R: Read + Seek,
{
    fn new(reader: R) -> Self {
        AvroReader {
            reader,
            rechunk: true,
            n_rows: None,
            columns: None,
            projection: None,
        }
    }

    fn set_rechunk(mut self, rechunk: bool) -> Self {
        self.rechunk = rechunk;
        self
    }

    fn finish(mut self) -> PolarsResult<DataFrame> {
        let rechunk = self.rechunk;
        let metadata =
            avro::avro_schema::read::read_metadata(&mut self.reader).map_err(convert_err)?;
        let schema = read::infer_schema(&metadata.record)?;

        if let Some(columns) = &self.columns {
            self.projection = Some(columns_to_projection(columns, &schema)?);
        }

        let (projection, projected_schema) = if let Some(projection) = self.projection {
            let mut prj = vec![false; schema.fields.len()];
            for &index in projection.iter() {
                prj[index] = true;
            }
            (Some(prj), apply_projection(&schema, &projection))
        } else {
            (None, schema.clone())
        };

        let avro_reader =
            avro::read::Reader::new(&mut self.reader, metadata, schema.fields, projection);

        finish_reader(
            avro_reader,
            rechunk,
            self.n_rows,
            None,
            &projected_schema,
            None,
        )
    }
}