List 未列出数据帧列

我有下面的数据框

df = pd.DataFrame({'sent':['Newyork is a beautiful city','the timing could not be better']})
df

我清理并过滤了下面的停止词

    stopwords = open('stop_words', 'r').read().split()
    df['cleaned'] = [x.lower().split() for x in df.sent]
    df['filtered'] = list(map(lambda line: list(filter(lambda word: word not in stopwords, line)), 
    df.cleaned)) 

   
              sent                         cleaned                            filtered
0   Newyork is a beautiful city     [newyork, is, a, beautiful, city]      [newyork, beautiful, city]
1   the timing could not be better  [the, timing, could, not, be, better]  [timing, be, better]

现在我想做的是，我需要在这个数据框中添加另一列，如下所示（取消列）

请帮忙，谢谢

     df_sent_new
0   newyork beautiful city
1   timing be better