tfidf = TfidfVectorizer(stop_words='english',ngram_range=(1,1))
中ngram_range(min,max)是指将text分成min,min+1,min+2,.........max 个不同的词组
比如'Python is useful'中ngram_range(1,3)之后可得到'Python' 'is' 'useful' 'Python is' 'is useful' 和'Python is useful'如果是ngram_range (1,1) 则只能得到单个单词'Python' 'is'和'useful'