def create_system_dict(df):
    """
    Reads a pandas dataFrame and creates a dictionary where the keys are the site ids and the values are a the list of
    systems for each site.
    :param df: pandas dataFrame with site and system information a `site` and a `system` column.
    :return: dictionary with systems associated to each site.
    """
    site_list = df['site'].unique().tolist()
    ss_dict = {}
    for site in site_list:
        systems_in_site = df[df['site'] == site]['system'].values.tolist()
        ss_dict[site] = systems_in_site
    return site_list, ss_dict