polars.Expr.map_alias#

Expr.map_alias(function: Callable[[str], str]) → Self[source]#

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

Parameters:

function: Function that maps a root name to a new name.

See also

alias
prefix
suffix

Examples

Remove a common suffix and convert to lower case.

>>> df = pl.DataFrame(
...     {
...         "A_reverse": [3, 2, 1],
...         "B_reverse": ["z", "y", "x"],
...     }
... )
>>> df.with_columns(
...     pl.all().reverse().map_alias(lambda c: c.rstrip("_reverse").lower())
... )
shape: (3, 4)
┌───────────┬───────────┬─────┬─────┐
│ A_reverse ┆ B_reverse ┆ a   ┆ b   │
│ ---       ┆ ---       ┆ --- ┆ --- │
│ i64       ┆ str       ┆ i64 ┆ str │
╞═══════════╪═══════════╪═════╪═════╡
│ 3         ┆ z         ┆ 1   ┆ x   │
│ 2         ┆ y         ┆ 2   ┆ y   │
│ 1         ┆ x         ┆ 3   ┆ z   │
└───────────┴───────────┴─────┴─────┘