CSV

Read & write

Reading a CSV file should look familiar:

Python Rust

read_csv

df = pl.read_csv("docs/assets/data/path.csv")

CsvReader · Available on feature csv

use polars::prelude::*;

let mut df = df!(
    "foo" => &[1, 2, 3],
    "bar" => &[None, Some("bak"), Some("baz")],
)
.unwrap();

let mut file = std::fs::File::create("docs/assets/data/path.csv").unwrap();
CsvWriter::new(&mut file).finish(&mut df).unwrap();

let df = CsvReadOptions::default()
    .try_into_reader_with_file_path(Some("docs/assets/data/path.csv".into()))
    .unwrap()
    .finish()
    .unwrap();

Writing a CSV file is similar with the write_csv function:

Python Rust

write_csv

df = pl.DataFrame({"foo": [1, 2, 3], "bar": [None, "bak", "baz"]})
df.write_csv("docs/assets/data/path.csv")

CsvWriter · Available on feature csv

let mut df = df!(
    "foo" => &[1, 2, 3],
    "bar" => &[None, Some("bak"), Some("baz")],
)
.unwrap();

let mut file = std::fs::File::create("docs/assets/data/path.csv").unwrap();
CsvWriter::new(&mut file).finish(&mut df).unwrap();

Scan

Polars allows you to scan a CSV input. Scanning delays the actual parsing of the file and instead returns a lazy computation holder called a LazyFrame.

Python Rust

scan_csv

df = pl.scan_csv("docs/assets/data/path.csv")

LazyCsvReader · Available on feature csv

let lf = LazyCsvReader::new("docs/assets/data/path.csv")
    .finish()
    .unwrap();

If you want to know why this is desirable, you can read more about these Polars optimizations here.