def extract_fips_years(pd_series):
    """
    Extract np.array of unique year ints from pd.series of 'FIPS_yyyy' strings
    :param series: pandas series
    :return: numpy array of year integers
    """
    years = (pd_series.str.extract(r'FIPS_(\d{4})')
             .dropna().squeeze().unique().astype(int))
    return years