polars.LazyFrame.pipe_with_schema#

LazyFrame.pipe_with_schema( function: Callable[[LazyFrame, Schema], LazyFrame], ) → LazyFrame[source]#

Allows to alter the lazy frame during the plan stage with the resolved schema.

In contrast to pipe, this method does not execute function immediately but only during the plan stage. This allows to use the resolved schema of the input to dynamically alter the lazy frame. This also means that any exceptions raised by function will only be emitted during the plan stage.

Warning

This functionality is considered unstable. It may be changed at any point without it being considered a breaking change.

Parameters:

function: Callable; will receive the frame as the first parameter and the resolved schema as the second parameter.

See also

pipe

Examples

>>> def cast_to_float_if_necessary(
...     lf: pl.LazyFrame, schema: pl.Schema
... ) -> pl.LazyFrame:
...     required_casts = [
...         pl.col(name).cast(pl.Float64)
...         for name, dtype in schema.items()
...         if not dtype.is_float()
...     ]
...     return lf.with_columns(required_casts)
>>> lf = pl.LazyFrame(
...     {"a": [1.0, 2.0], "b": ["1.0", "2.5"], "c": [2.0, 3.0]},
...     schema={"a": pl.Float64, "b": pl.String, "c": pl.Float32},
... )
>>> lf.pipe_with_schema(cast_to_float_if_necessary).collect()
shape: (2, 3)
┌─────┬─────┬─────┐
│ a   ┆ b   ┆ c   │
│ --- ┆ --- ┆ --- │
│ f64 ┆ f64 ┆ f32 │
╞═════╪═════╪═════╡
│ 1.0 ┆ 1.0 ┆ 2.0 │
│ 2.0 ┆ 2.5 ┆ 3.0 │
└─────┴─────┴─────┘