Function map_multiple

pub fn map_multiple<F, E>(function: F, expr: E, output_type: GetOutput) -> Expr
where
    F: Fn(&mut [Column]) -> PolarsResult<Option<Column>> + 'static + Send + Sync,
    E: AsRef<[Expr]>,

Apply a function/closure over multiple columns once the logical plan get executed.

This function is very similar to [apply_mul], but differs in how it handles aggregations.

• map_mul should be used for operations that are independent of groups, e.g. multiply * 2, or raise to the power
• apply_mul should be used for operations that work on a group of data. e.g. sum, count, etc.

It is the responsibility of the caller that the schema is correct by giving the correct output_type. If None given the output type of the input expr is used.