Using apply in polars

Question

I am trying to create a new column using apply in polars.

For this, I tried the following operation:

df = df.with_columns(
    pl.col("AH_PROC_REALIZADO")
    .apply(get_procedure_description)
    .alias("proced_descr")
)

But I'm getting the error:

AttributeError: 'Expr' object has no attribute 'apply'

The function I am trying to apply looks as follows.

def get_procedure_description(cod):
    proceds = {
        '41612': 'CIRURGIA ONCOLOGICA',
        '30401': 'RADIOTERAPIA',
        ...
    }

    for proced in proceds.keys():
        if cod[: len(proced)] == proced:
            return proceds[proced]
        
    return None

Answer 1

pl.Expr.apply was deprecated in favour of pl.Expr.map_elements in Polars release 0.19.0. Recently, pl.Expr.apply was removed in the release of Polars 1.0.0.

You can adapt your code to the new version as follows.

df.with_columns(
    pl.col("AH_PROC_REALIZADO")
    .map_elements(get_procedure_description, return_dtype=pl.String)
    .alias("proced_descr")
)