rerank the two vectors by
    min aggregrate rank, reorder

def _aggregrate_scores(its,tss,num_sentences):
    """rerank the two vectors by
    min aggregrate rank, reorder"""
    final = []
    for i,el in enumerate(its):
        for j, le in enumerate(tss):
            if el[2] == le[2]:
                assert el[1] == le[1]
                final.append((el[1],i+j,el[2]))
    _final = sorted(final, key = lambda tup: tup[1])[:num_sentences]
    return sorted(_final, key = lambda tup: tup[0])