def compare(self, event):
        raise NotImplementedError()
Right now the fields supported are 'tags_id_stories' or 'tags_id_story_sentences'
dataset/ETHPy150Open Yelp/elastalert/elastalert/ruletypes.py/CompareRule.compare--crossover with--dataset/ETHPy150Open c4fcm/MediaCloud-API-Client/mediacloud/api.py/MediaCloud.sentenceFieldCount