def top_brands(data, topn=50):
    """
    get top brands dataframe (review count 기준)
    :param data: total dataframe
    :param topn: num of top brands
    :return: top brands data, top brands list
    """
    grouped = data.groupby('brand')
    s = grouped.count()
    brand_name = s.sort_values('asin', ascending=False).index[:topn]
    return data[data['brand'].isin(brand_name)], brand_name