def jaccard_similarity(b1, b2):
    """Jaccard similarity between two set b1 and b2
    :param b1: set of index if there is a rate for business b1
    :param b2: set of index if there is a rate for business b2
    :return: jaccard similarity of two sets
    """
    return len(b1.intersection(b2))/len(b1.union(b2))