def all_providers_cnpj(df):
    """
    Return CPF/CNPJ of all providers
    in database.
    """
    cnpj_list = []

    for _, items in df.groupby('PRONAC'):
        unique_cnpjs = items['nrCNPJCPF'].unique()
        cnpj_list += list(unique_cnpjs)

    return pd.DataFrame(cnpj_list)
Return CPF/CNPJ of all providers
    in database.