polars.Expr.prefix#

Expr.prefix(prefix: str) → Self[source]#
Add a prefix to the root column name of the expression.
Examples
>>> df = pl.DataFrame(
...     {
...         "A": [1, 2, 3, 4, 5],
...         "fruits": ["banana", "banana", "apple", "apple", "banana"],
...         "B": [5, 4, 3, 2, 1],
...         "cars": ["beetle", "audi", "beetle", "beetle", "beetle"],
...     }
... )
>>> df
shape: (5, 4)
┌─────┬────────┬─────┬────────┐
│ A   ┆ fruits ┆ B   ┆ cars   │
│ --- ┆ ---    ┆ --- ┆ ---    │
│ i64 ┆ str    ┆ i64 ┆ str    │
╞═════╪════════╪═════╪════════╡
│ 1   ┆ banana ┆ 5   ┆ beetle │
│ 2   ┆ banana ┆ 4   ┆ audi   │
│ 3   ┆ apple  ┆ 3   ┆ beetle │
│ 4   ┆ apple  ┆ 2   ┆ beetle │
│ 5   ┆ banana ┆ 1   ┆ beetle │
└─────┴────────┴─────┴────────┘
>>> df.select(
...     [
...         pl.all(),
...         pl.all().reverse().prefix("reverse_"),
...     ]
... )
shape: (5, 8)
┌─────┬────────┬─────┬────────┬───────────┬────────────────┬───────────┬──────────────┐
│ A   ┆ fruits ┆ B   ┆ cars   ┆ reverse_A ┆ reverse_fruits ┆ reverse_B ┆ reverse_cars │
│ --- ┆ ---    ┆ --- ┆ ---    ┆ ---       ┆ ---            ┆ ---       ┆ ---          │
│ i64 ┆ str    ┆ i64 ┆ str    ┆ i64       ┆ str            ┆ i64       ┆ str          │
╞═════╪════════╪═════╪════════╪═══════════╪════════════════╪═══════════╪══════════════╡
│ 1   ┆ banana ┆ 5   ┆ beetle ┆ 5         ┆ banana         ┆ 1         ┆ beetle       │
│ 2   ┆ banana ┆ 4   ┆ audi   ┆ 4         ┆ apple          ┆ 2         ┆ beetle       │
│ 3   ┆ apple  ┆ 3   ┆ beetle ┆ 3         ┆ apple          ┆ 3         ┆ beetle       │
│ 4   ┆ apple  ┆ 2   ┆ beetle ┆ 2         ┆ banana         ┆ 4         ┆ audi         │
│ 5   ┆ banana ┆ 1   ┆ beetle ┆ 1         ┆ banana         ┆ 5         ┆ beetle       │
└─────┴────────┴─────┴────────┴───────────┴────────────────┴───────────┴──────────────┘