Getting started

Installation

Installing and using Polars is just a simple pip install, cargo add, or yarn add away.

$ # Installing for python
$ pip install polars
$ # Installing into a Rust project
$ cargo add polars
$ # Installing for Node
$ yarn add nodejs-polars

All binaries are pre-built for Python v3.6+.

Quick start

Below we show a simple snippet that parses a CSV file, filters it, and finishes with a groupby operation. This example is presented in python only, as the "eager" API is not the preferred model in Rust.

import polars as pl

df = pl.read_csv("https://j.mp/iriscsv")
print(df.filter(pl.col("sepal_length") > 5)
      .groupby("species")
      .agg(pl.all().sum())
)

The snippet above will output:

shape: (3, 5)
╭──────────────┬──────────────────┬─────────────────┬──────────────────┬─────────────────╮
│ species      ┆ sepal_length_sum ┆ sepal_width_sum ┆ petal_length_sum ┆ petal_width_sum │
│ ---          ┆ ---              ┆ ---             ┆ ---              ┆ ---             │
│ str          ┆ f64              ┆ f64             ┆ f64              ┆ f64             │
╞══════════════╪══════════════════╪═════════════════╪══════════════════╪═════════════════╡
│ "virginica"  ┆ 324.5            ┆ 146.2           ┆ 273.1            ┆ 99.6            │
├╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┤
│ "versicolor" ┆ 281.9            ┆ 131.8           ┆ 202.9            ┆ 63.3            │
├╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┤
│ "setosa"     ┆ 116.9            ┆ 81.7            ┆ 33.2             ┆ 6.1             │
╰──────────────┴──────────────────┴─────────────────┴──────────────────┴─────────────────╯

As we can see, Polars pretty-prints the output object, including the column name and datatype as headers.

Lazy quick start

If we want to run this query in lazy Polars we'd write:

import polars as pl

print(
    pl.read_csv("https://j.mp/iriscsv")
    .lazy()
    .filter(pl.col("sepal_length") > 5)
    .groupby("species")
    .agg(pl.all().sum())
    .collect()
)

use color_eyre::{Result};
use polars::prelude::*;
use reqwest::blocking::Client;

fn main() -> Result<()> { 
    let data: Vec<u8> = Client::new()
        .get("https://j.mp/iriscsv")
        .send()?
        .text()?
        .bytes()
        .collect();

    let df = CsvReader::new(Cursor::new(data))
        .has_header(true)
        .finish()?
        .lazy()
        .filter(col("sepal_length").gt(5))
        .groupby([col("species")])
        .agg([col("*").sum()])
        .collect()?;

    println!("{:?}", df);

    Ok(())
}

When the data is stored locally, we can also use scan_csv in Python, or LazyCsvReader in Rust to run the query in lazy polars.

References

If you want to dive right into the Python API docs, check the the reference docs. Alternatively, the Rust API docs are available on docs.rs.

Lazy API

The lazy API builds a query plan. Nothing is executed until you explicitly ask Polars to execute the query (via LazyFrame.collect(), or LazyFrame.fetch()). This provides Polars with the entire context of the query, allowing optimizations and choosing the fastest algorithm given that context.

Going from eager to lazy is often as simple as starting your query with .lazy() and ending with .collect().

So the eager snippet above would become:

(
    df.lazy()
    .filter(pl.col("sepal_length") > 5)
    .groupby("species")
    .agg(pl.all().sum())
    .collect()
)

let df = df
    .lazy()
    .filter(col("sepal_length").gt(5))
    .groupby([col("species")])
    .agg([col("*" ).sum()])
    .collect()?;