polars.Expr.over#
- Expr.over(expr: IntoExpr | Iterable[IntoExpr], *more_exprs: IntoExpr) Self [source]#
Compute expressions over the given groups.
This expression is similar to performing a groupby aggregation and joining the result back into the original dataframe.
The outcome is similar to how window functions work in PostgreSQL.
- Parameters:
- expr
Column(s) to group by. Accepts expression input. Strings are parsed as column names.
- *more_exprs
Additional columns to group by, specified as positional arguments.
Examples
Pass the name of a column to compute the expression over that column.
>>> df = pl.DataFrame( ... { ... "a": ["a", "a", "b", "b", "b"], ... "b": [1, 2, 3, 5, 3], ... "c": [5, 4, 3, 2, 1], ... } ... ) >>> df.with_columns(pl.col("c").max().over("a").suffix("_max")) shape: (5, 4) ┌─────┬─────┬─────┬───────┐ │ a ┆ b ┆ c ┆ c_max │ │ --- ┆ --- ┆ --- ┆ --- │ │ str ┆ i64 ┆ i64 ┆ i64 │ ╞═════╪═════╪═════╪═══════╡ │ a ┆ 1 ┆ 5 ┆ 5 │ │ a ┆ 2 ┆ 4 ┆ 5 │ │ b ┆ 3 ┆ 3 ┆ 3 │ │ b ┆ 5 ┆ 2 ┆ 3 │ │ b ┆ 3 ┆ 1 ┆ 3 │ └─────┴─────┴─────┴───────┘
Expression input is supported.
>>> df.with_columns(pl.col("c").max().over(pl.col("b") // 2).suffix("_max")) shape: (5, 4) ┌─────┬─────┬─────┬───────┐ │ a ┆ b ┆ c ┆ c_max │ │ --- ┆ --- ┆ --- ┆ --- │ │ str ┆ i64 ┆ i64 ┆ i64 │ ╞═════╪═════╪═════╪═══════╡ │ a ┆ 1 ┆ 5 ┆ 5 │ │ a ┆ 2 ┆ 4 ┆ 4 │ │ b ┆ 3 ┆ 3 ┆ 4 │ │ b ┆ 5 ┆ 2 ┆ 2 │ │ b ┆ 3 ┆ 1 ┆ 4 │ └─────┴─────┴─────┴───────┘
Group by multiple columns by passing a list of column names or expressions.
>>> df.with_columns(pl.col("c").min().over(["a", "b"]).suffix("_min")) shape: (5, 4) ┌─────┬─────┬─────┬───────┐ │ a ┆ b ┆ c ┆ c_min │ │ --- ┆ --- ┆ --- ┆ --- │ │ str ┆ i64 ┆ i64 ┆ i64 │ ╞═════╪═════╪═════╪═══════╡ │ a ┆ 1 ┆ 5 ┆ 5 │ │ a ┆ 2 ┆ 4 ┆ 4 │ │ b ┆ 3 ┆ 3 ┆ 1 │ │ b ┆ 5 ┆ 2 ┆ 2 │ │ b ┆ 3 ┆ 1 ┆ 1 │ └─────┴─────┴─────┴───────┘
Or use positional arguments to group by multiple columns in the same way.
>>> df.with_columns(pl.col("c").min().over("a", pl.col("b") % 2).suffix("_min")) shape: (5, 4) ┌─────┬─────┬─────┬───────┐ │ a ┆ b ┆ c ┆ c_min │ │ --- ┆ --- ┆ --- ┆ --- │ │ str ┆ i64 ┆ i64 ┆ i64 │ ╞═════╪═════╪═════╪═══════╡ │ a ┆ 1 ┆ 5 ┆ 5 │ │ a ┆ 2 ┆ 4 ┆ 4 │ │ b ┆ 3 ┆ 3 ┆ 1 │ │ b ┆ 5 ┆ 2 ┆ 1 │ │ b ┆ 3 ┆ 1 ┆ 1 │ └─────┴─────┴─────┴───────┘