polars.Expr.map#
- Expr.map(function: Callable[[Series], Series | Any], return_dtype: PolarsDataType | None = None, *, agg_list: bool = False) Self [source]#
Apply a custom python function to a Series or sequence of Series.
The output of this custom function must be a Series. If you want to apply a custom function elementwise over single values, see
apply()
. A use case formap
is when you want to transform an expression with a third-party library.Read more in the book.
- Parameters:
- function
Lambda/ function to apply.
- return_dtype
Dtype of the output Series.
- agg_list
Aggregate list
Examples
>>> df = pl.DataFrame( ... { ... "sine": [0.0, 1.0, 0.0, -1.0], ... "cosine": [1.0, 0.0, -1.0, 0.0], ... } ... ) >>> df.select(pl.all().map(lambda x: x.to_numpy().argmax())) shape: (1, 2) ┌──────┬────────┐ │ sine ┆ cosine │ │ --- ┆ --- │ │ i64 ┆ i64 │ ╞══════╪════════╡ │ 1 ┆ 0 │ └──────┴────────┘