polars.Expr.interpolate_by

Expr.interpolate_by(
    by: IntoExpr,
) → Expr

Fill null values using interpolation based on another column.

Nulls at the beginning and end of the series remain null.

engine:In Memory

Parameters:

by

Column to interpolate values based on.

Examples

Fill null values using linear interpolation.

>>> df = pl.DataFrame(
...     {
...         "a": [1, None, None, 3],
...         "b": [1, 2, 7, 8],
...     }
... )
>>> df.with_columns(a_interpolated=pl.col("a").interpolate_by("b"))
shape: (4, 3)
┌──────┬─────┬────────────────┐
│ a    ┆ b   ┆ a_interpolated │
│ ---  ┆ --- ┆ ---            │
│ i64  ┆ i64 ┆ f64            │
╞══════╪═════╪════════════════╡
│ 1    ┆ 1   ┆ 1.0            │
│ null ┆ 2   ┆ 1.285714       │
│ null ┆ 7   ┆ 2.714286       │
│ 3    ┆ 8   ┆ 3.0            │
└──────┴─────┴────────────────┘