polars.Expr.map_alias#

Expr.map_alias(f: Callable[[str], str]) Expr[source]#

Rename the output of an expression by mapping a function over the root name.

Parameters:
f

Function that maps root name to new name.

Examples

>>> df = pl.DataFrame(
...     {
...         "A": [1, 2],
...         "B": [3, 4],
...     }
... )
>>> df.select(
...     pl.all().reverse().map_alias(lambda colName: colName + "_reverse")
... )
shape: (2, 2)
┌───────────┬───────────┐
│ A_reverse ┆ B_reverse │
│ ---       ┆ ---       │
│ i64       ┆ i64       │
╞═══════════╪═══════════╡
│ 2         ┆ 4         │
├╌╌╌╌╌╌╌╌╌╌╌┼╌╌╌╌╌╌╌╌╌╌╌┤
│ 1         ┆ 3         │
└───────────┴───────────┘