Basic operators

This section describes how to use basic operators (e.g. addition, subtraction) in conjunction with Expressions. We will provide various examples using different themes in the context of the following dataframe.

Note

In Rust and Python it is possible to use the operators directly (as in + - * / < >) as the language allows operator overloading. For instance, the operator + translates to the .add() method. You can choose the one you prefer.

Python Rust

DataFrame

df = pl.DataFrame(
    {
        "nrs": [1, 2, 3, None, 5],
        "names": ["foo", "ham", "spam", "egg", None],
        "random": np.random.rand(5),
        "groups": ["A", "A", "B", "C", "B"],
    }
)
print(df)

DataFrame

use rand::{thread_rng, Rng};

let mut arr = [0f64; 5];
thread_rng().fill(&mut arr);

let df = df! (
    "nrs" => &[Some(1), Some(2), Some(3), None, Some(5)],
    "names" => &[Some("foo"), Some("ham"), Some("spam"), Some("eggs"), None],
    "random" => &arr,
    "groups" => &["A", "A", "B", "C", "B"],
)?;

println!("{}", &df);

shape: (5, 4)
┌──────┬───────┬──────────┬────────┐
│ nrs  ┆ names ┆ random   ┆ groups │
│ ---  ┆ ---   ┆ ---      ┆ ---    │
│ i64  ┆ str   ┆ f64      ┆ str    │
╞══════╪═══════╪══════════╪════════╡
│ 1    ┆ foo   ┆ 0.154163 ┆ A      │
│ 2    ┆ ham   ┆ 0.74005  ┆ A      │
│ 3    ┆ spam  ┆ 0.263315 ┆ B      │
│ null ┆ egg   ┆ 0.533739 ┆ C      │
│ 5    ┆ null  ┆ 0.014575 ┆ B      │
└──────┴───────┴──────────┴────────┘

Numerical

Python Rust

operators

df_numerical = df.select(
    (pl.col("nrs") + 5).alias("nrs + 5"),
    (pl.col("nrs") - 5).alias("nrs - 5"),
    (pl.col("nrs") * pl.col("random")).alias("nrs * random"),
    (pl.col("nrs") / pl.col("random")).alias("nrs / random"),
)
print(df_numerical)

let df_numerical = df
    .clone()
    .lazy()
    .select([
        (col("nrs") + lit(5)).alias("nrs + 5"),
        (col("nrs") - lit(5)).alias("nrs - 5"),
        (col("nrs") * col("random")).alias("nrs * random"),
        (col("nrs") / col("random")).alias("nrs / random"),
    ])
    .collect()?;
println!("{}", &df_numerical);

shape: (5, 4)
┌─────────┬─────────┬──────────────┬──────────────┐
│ nrs + 5 ┆ nrs - 5 ┆ nrs * random ┆ nrs / random │
│ ---     ┆ ---     ┆ ---          ┆ ---          │
│ i64     ┆ i64     ┆ f64          ┆ f64          │
╞═════════╪═════════╪══════════════╪══════════════╡
│ 6       ┆ -4      ┆ 0.154163     ┆ 6.486647     │
│ 7       ┆ -3      ┆ 1.480099     ┆ 2.702521     │
│ 8       ┆ -2      ┆ 0.789945     ┆ 11.393198    │
│ null    ┆ null    ┆ null         ┆ null         │
│ 10      ┆ 0       ┆ 0.072875     ┆ 343.054056   │
└─────────┴─────────┴──────────────┴──────────────┘

Logical

Python Rust

operators

df_logical = df.select(
    (pl.col("nrs") > 1).alias("nrs > 1"),
    (pl.col("random") <= 0.5).alias("random < .5"),
    (pl.col("nrs") != 1).alias("nrs != 1"),
    (pl.col("nrs") == 1).alias("nrs == 1"),
    ((pl.col("random") <= 0.5) & (pl.col("nrs") > 1)).alias("and_expr"),  # and
    ((pl.col("random") <= 0.5) | (pl.col("nrs") > 1)).alias("or_expr"),  # or
)
print(df_logical)

let df_logical = df
    .clone()
    .lazy()
    .select([
        col("nrs").gt(1).alias("nrs > 1"),
        col("random").lt_eq(0.5).alias("random < .5"),
        col("nrs").neq(1).alias("nrs != 1"),
        col("nrs").eq(1).alias("nrs == 1"),
        (col("random").lt_eq(0.5))
            .and(col("nrs").gt(1))
            .alias("and_expr"), // and
        (col("random").lt_eq(0.5))
            .or(col("nrs").gt(1))
            .alias("or_expr"), // or
    ])
    .collect()?;
println!("{}", &df_logical);

shape: (5, 6)
┌─────────┬─────────────┬──────────┬──────────┬──────────┬─────────┐
│ nrs > 1 ┆ random < .5 ┆ nrs != 1 ┆ nrs == 1 ┆ and_expr ┆ or_expr │
│ ---     ┆ ---         ┆ ---      ┆ ---      ┆ ---      ┆ ---     │
│ bool    ┆ bool        ┆ bool     ┆ bool     ┆ bool     ┆ bool    │
╞═════════╪═════════════╪══════════╪══════════╪══════════╪═════════╡
│ false   ┆ true        ┆ false    ┆ true     ┆ false    ┆ true    │
│ true    ┆ false       ┆ true     ┆ false    ┆ false    ┆ true    │
│ true    ┆ true        ┆ true     ┆ false    ┆ true     ┆ true    │
│ null    ┆ false       ┆ null     ┆ null     ┆ false    ┆ null    │
│ true    ┆ true        ┆ true     ┆ false    ┆ true     ┆ true    │
└─────────┴─────────────┴──────────┴──────────┴──────────┴─────────┘