Function gather_and_postprocess 

pub fn gather_and_postprocess(
    build: DataFrame,
    probe: DataFrame,
    gather_build: Option<&[u32]>,
    gather_probe: Option<&[u32]>,
    df_builders: &mut Option<(DataFrameBuilder, DataFrameBuilder)>,
    args: &JoinArgs,
    left_on: &[PlSmallStr],
    right_on: &[PlSmallStr],
    left_is_build: bool,
    output_schema: &Schema<DataType>,
) -> Result<DataFrame, PolarsError>

Available on crate feature polars-ops only.