polars.coalesce#

polars.coalesce(
exprs: IntoExpr | Iterable[IntoExpr],
*more_exprs: IntoExpr,
eager: bool = False,
) → Expr | Series[source]#

Folds the columns from left to right, keeping the first non-null value.

Parameters:
exprs

Columns to coalesce. Accepts expression input. Strings are parsed as column names, other non-expression inputs are parsed as literals.

*more_exprs

Additional columns to coalesce, specified as positional arguments.

eager

Evaluate immediately and return a Series; this requires that at least one of the given arguments is a Series. If set to False (default), return an expression instead.

Examples

>>> df = pl.DataFrame(
...     {
...         "a": [1, None, None, None],
...         "b": [1, 2, None, None],
...         "c": [5, None, 3, None],
...     }
... )

>>> df.with_columns(pl.coalesce("a", "b", "c", 10).alias("d"))
shape: (4, 4)
┌──────┬──────┬──────┬─────┐
│ a    ┆ b    ┆ c    ┆ d   │
│ ---  ┆ ---  ┆ ---  ┆ --- │
│ i64  ┆ i64  ┆ i64  ┆ i64 │
╞══════╪══════╪══════╪═════╡
│ 1    ┆ 1    ┆ 5    ┆ 1   │
│ null ┆ 2    ┆ null ┆ 2   │
│ null ┆ null ┆ 3    ┆ 3   │
│ null ┆ null ┆ null ┆ 10  │
└──────┴──────┴──────┴─────┘

>>> df.with_columns(pl.coalesce(pl.col(["a", "b", "c"]), 10.0).alias("d"))
shape: (4, 4)
┌──────┬──────┬──────┬──────┐
│ a    ┆ b    ┆ c    ┆ d    │
│ ---  ┆ ---  ┆ ---  ┆ ---  │
│ i64  ┆ i64  ┆ i64  ┆ f64  │
╞══════╪══════╪══════╪══════╡
│ 1    ┆ 1    ┆ 5    ┆ 1.0  │
│ null ┆ 2    ┆ null ┆ 2.0  │
│ null ┆ null ┆ 3    ┆ 3.0  │
│ null ┆ null ┆ null ┆ 10.0 │
└──────┴──────┴──────┴──────┘

>>> s1 = pl.Series("a", [None, 2, None])
>>> s2 = pl.Series("b", [1, None, 3])
>>> pl.coalesce(s1, s2, eager=True)
shape: (3,)
Series: 'a' [i64]
[
    1
    2
    3
]
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