polars.Expr.prefix#

Expr.prefix(prefix: str) → Self[source]#

Add a prefix to the root column name of the expression.

Parameters:

prefix: Prefix to add to the root column name.

See also

suffix

Notes

This will undo any previous renaming operations on the expression.

Due to implementation constraints, this method can only be called as the last expression in a chain.

Examples

>>> df = pl.DataFrame(
...     {
...         "a": [1, 2, 3],
...         "b": ["x", "y", "z"],
...     }
... )
>>> df.with_columns(pl.all().reverse().prefix("reverse_"))
shape: (3, 4)
┌─────┬─────┬───────────┬───────────┐
│ a   ┆ b   ┆ reverse_a ┆ reverse_b │
│ --- ┆ --- ┆ ---       ┆ ---       │
│ i64 ┆ str ┆ i64       ┆ str       │
╞═════╪═════╪═══════════╪═══════════╡
│ 1   ┆ x   ┆ 3         ┆ z         │
│ 2   ┆ y   ┆ 2         ┆ y         │
│ 3   ┆ z   ┆ 1         ┆ x         │
└─────┴─────┴───────────┴───────────┘