Crate polars_rows_iter

Source
Expand description

§Polars rows iterator

Simple and convenient iteration of polars dataframe rows.

§Example: Dataframe without None/null values:
use polars::prelude::*;
use polars_rows_iter::*;

#[derive(Debug, FromDataFrameRow)]
#[derive(PartialEq)] // for assert_eq
struct MyRow<'a>
{
    #[column("col_a")]
    a: i32,
    // the column name defaults to the field name if no explicit name given
    col_b: &'a str
}

let df = df!(
        "col_a" => [1i32, 2, 3, 4, 5],
        "col_b" => ["a", "b", "c", "d", "e"]
    ).unwrap();

let rows_iter = df.rows_iter::<MyRow>().unwrap(); // ready to use row iterator
// unwrap rows and collect to vector for assert_eq
let rows_vec = rows_iter.map(|row|row.unwrap()).collect::<Vec<MyRow>>();

assert_eq!(
    rows_vec,
    [
        MyRow { a: 1, col_b: "a" },
        MyRow { a: 2, col_b: "b" },
        MyRow { a: 3, col_b: "c" },
        MyRow { a: 4, col_b: "d" },
        MyRow { a: 5, col_b: "e" },
    ]
);

Every row is wrapped with a PolarsError, in case of an unexpected null value the row creation fails and the iterator returns an Err(…) for the row. One can decide to cancel the iteration or to skip the affected row.

§Example: Dataframe with valid None/null values:
use polars::prelude::*;
use polars_rows_iter::*;

#[derive(Debug, FromDataFrameRow)]
#[derive(PartialEq)] // for assert_eq
struct MyRow<'a>
{
    col_a: i32,
    col_b: Option<&'a str>
}

let df = df!(
        "col_a" => [1i32, 2, 3, 4, 5],
        "col_b" => [Some("a"), None, Some("c"), None, Some("e")]
    ).unwrap();

let rows_iter = df.rows_iter::<MyRow>().unwrap(); // ready to use row iterator
// unwrap rows and collect to vector for assert_eq
let rows_vec = rows_iter.map(|row|row.unwrap()).collect::<Vec<MyRow>>();

assert_eq!(
    rows_vec,
    [
        MyRow { col_a: 1, col_b: Some("a") },
        MyRow { col_a: 2, col_b: None },
        MyRow { col_a: 3, col_b: Some("c") },
        MyRow { col_a: 4, col_b: None },
        MyRow { col_a: 5, col_b: Some("e") },
    ]
);

§Limitations

Currently supports only primitive and string/categorical types

Traits§

Derive Macros§