在 lambda 函数中使用列表理解？

Question

我有一个包含 n-gram 元组列表的数据框。 我想将元组列表转换为字符串列表。 为此，我试图在我的 lambda 函数中使用列表理解。 但是，我不断收到错误消息，说我的列表未定义。

id     n_grams
 1     [(thanks), (thanks, past), (thanks, past, blue)]
 2     [(support), (support, arm), (support, arm, brace), (support, arm, brace, left)]
 3     [(blue), (blue, sky), (blue, sky, rain)]
 4     [(breaking), (breaking, news), (breaking, news, fire), (breaking, news, fire, aparment)]

我试图得到：

id     n_grams
 1     ["thanks", "thanks past", "thanks past blue"]
 2     ["support", "support arm", "support arm brace", "support arm brace left"]
 3     ["blue", "blue sky", "blue sky rain"]
 4     ["breaking", "breaking news", "breaking news fire", "breaking news fire apartment"]

我试过了：

data['n_grams'] = data.n_grams.apply(lambda row: " ".join(x) for x in row)

但我不断收到错误消息：

NameError: name 'row' is not defined

Answer 1

感谢 rdas 的评论，解决方案只是使用硬括号：

data['n_grams'] = data.n_grams.apply(lambda row: [" ".join(x) for x in row])

Answer 2

这应该工作：

df.n_grams.apply(lambda row: [" ".join(x) for x in row])