将pandas列中的列表列表转换为字符串

Question

如何将包含列表列表的pandas df列转换为字符串。 df中列“类别”的片段

[['Electronics', 'Computers & Accessories', 'Cables & Accessories', 'Cables & Interconnects', 'USB Cables'], ['Video Games', 'Sony PSP']]
[['Video Games', 'PlayStation 3', 'Accessories', 'Controllers', 'Gamepads']]
[['Cell Phones & Accessories', 'Accessories', 'Chargers', 'Travel Chargers'], ['Video Games', 'Nintendo DS']]

我尝试了以下代码：

df.loc[:,"categories"]=[item for sublist in df.loc[:,"categories"] for item in sublist]

但它给了我一个错误。有没有其他方法这样做？

ValueError：值的长度与索引的长度不匹配

预期专栏：

'Electronics', 'Computers & Accessories', 'Cables & Accessories', 'Cables & Interconnects', 'USB Cables','Video Games', 'Sony PSP'
'Video Games', 'PlayStation 3', 'Accessories', 'Controllers', 'Gamepads'
'Cell Phones & Accessories', 'Accessories', 'Chargers', 'Travel Chargers','Video Games', 'Nintendo DS'

Answer 1

使用嵌套生成器与join：

df["categories"]=[', '.join(item for sublist in x for item in sublist) for x in df["categories"]]

如果在较大的DataFrame中表现很重要：

from  itertools import chain

df["categories"] = [', '.join(chain.from_iterable(x)) for x in df["categories"]]

print (df)
                                          categories
0  Electronics, Computers & Accessories, Cables &...
1  Video Games, PlayStation 3, Accessories, Contr...
2  Cell Phones & Accessories, Accessories, Charge...

时间:(在实际数据中应该是不同的，最好先测试一下）：

df = pd.concat([df] * 10000, ignore_index=True)


In [45]: %timeit df["c1"]=[', '.join(item for sublist in x for item in sublist) for x in df["categories"]]
39 ms ± 706 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)

In [46]: %timeit df["c2"]=[', '.join(chain.from_iterable(x)) for x in df["categories"]]
22.1 ms ± 258 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)

In [47]: %timeit df['c3'] = df["categories"].apply(lambda x: ', '.join(str(r) for v in x for r in v))
66.7 ms ± 695 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)

Answer 2

你需要列表理解

df['col'] = df.col.apply(lambda x: ', '.join(str(r) for v in x for r in v))

输出：

    col
0   Electronics, Computers & Accessories, Cables &...
1   Video Games, PlayStation 3, Accessories, Contr...
2   Cell Phones & Accessories, Accessories, Charge...