def category_join_reducer(self, business_id, reviews_or_categories):
        categories = None
        reviews = []

        for data_type, data in reviews_or_categories:
            if data_type == 'review':
                reviews.append(data)
            else:
                categories = data

        # no categories found, skip this
        if not categories:
            return

        for category in categories:
            for review_positivity in reviews:
                yield category, (business_id, review_positivity)
Take in business_id, ((review text and rating) or category information), emit
dataset/ETHPy150Open Yelp/dataset-examples/positive_category_words/weighted_category_positivity.py/WeightedPositiveWords.category_join_reducer