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 │ └─────┴────────┴─────┴────────┴───────────┴────────────────┴───────────┴──────────────┘