polars.Expr.fill_null

Expr.fill_null(
    value: Any | Expr | None = None,
    strategy: FillNullStrategy | None = None,
    limit: int | None = None,
) → Expr

Fill null values using the specified value or strategy.

To interpolate over null values see interpolate. See the examples below to fill nulls with an expression.

engine:In MemoryStreaming

Parameters:

value

Value used to fill null values.

strategy{None, ‘forward’, ‘backward’, ‘min’, ‘max’, ‘mean’, ‘zero’, ‘one’}

Strategy used to fill null values.

limit

Number of consecutive null values to fill when using the ‘forward’ or ‘backward’ strategy.

See also

backward_fill

fill_nan

forward_fill

Notes

A null value is not the same as a NaN value. To fill NaN values, use fill_nan().

Examples

>>> df = pl.DataFrame(
...     {
...         "a": [1, 2, None],
...         "b": [4, None, 6],
...     }
... )
>>> df.with_columns(pl.col("b").fill_null(strategy="zero"))
shape: (3, 2)
┌──────┬─────┐
│ a    ┆ b   │
│ ---  ┆ --- │
│ i64  ┆ i64 │
╞══════╪═════╡
│ 1    ┆ 4   │
│ 2    ┆ 0   │
│ null ┆ 6   │
└──────┴─────┘
>>> df.with_columns(pl.col("b").fill_null(99))
shape: (3, 2)
┌──────┬─────┐
│ a    ┆ b   │
│ ---  ┆ --- │
│ i64  ┆ i64 │
╞══════╪═════╡
│ 1    ┆ 4   │
│ 2    ┆ 99  │
│ null ┆ 6   │
└──────┴─────┘
>>> df.with_columns(pl.col("b").fill_null(strategy="forward"))
shape: (3, 2)
┌──────┬─────┐
│ a    ┆ b   │
│ ---  ┆ --- │
│ i64  ┆ i64 │
╞══════╪═════╡
│ 1    ┆ 4   │
│ 2    ┆ 4   │
│ null ┆ 6   │
└──────┴─────┘
>>> df.with_columns(pl.col("b").fill_null(pl.col("b").median()))
shape: (3, 2)
┌──────┬─────┐
│ a    ┆ b   │
│ ---  ┆ --- │
│ i64  ┆ f64 │
╞══════╪═════╡
│ 1    ┆ 4.0 │
│ 2    ┆ 5.0 │
│ null ┆ 6.0 │
└──────┴─────┘
>>> df.with_columns(pl.all().fill_null(pl.all().median()))
shape: (3, 2)
┌─────┬─────┐
│ a   ┆ b   │
│ --- ┆ --- │
│ f64 ┆ f64 │
╞═════╪═════╡
│ 1.0 ┆ 4.0 │
│ 2.0 ┆ 5.0 │
│ 1.5 ┆ 6.0 │
└─────┴─────┘