How to format expr in polars by rust?

Question

Polars python, format a column like this

df = pl.DataFrame({
    "a": [0.15, 0.25]
})
result = df.with_columns(
    pl.format("{}%", (pl.col("a") * 100).round(1))
)
print(result)

output

shape: (2, 1)
┌───────┐
│ a     │
│ ---   │
│ str   │
╞═══════╡
│ 15.0% │
│ 25.0% │
└───────┘

How to do this with polars rust?

user459872 · Accepted Answer · 2025-03-11 17:43:27Z

3

You can format it using format_str. You must also enable lazy, concat_str, strings, round_series features in Cargo.toml file.

use polars::prelude::*;

fn main() {
    let mut df = df!(
        "a" => &[0.15, 0.25]
    )
    .unwrap();

    let format_str = [format_str("{}%", [(col("a") * lit(100)).round(1)]).unwrap()];
    let new = df.lazy().with_columns(format_str).collect().unwrap();
    println!("{:?}", new);
}

This will give you the following output.

┌───────┐
│ a     │
│ ---   │
│ str   │
╞═══════╡
│ 15.0% │
│ 25.0% │
└───────┘

edited Mar 11 at 17:43

answered Mar 11 at 17:20

user459872

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