pandas 数据框:set_index和inplace = True会返回NoneType，为什么? [英] Pandas dataframe: set_index with inplace=True returns a NoneType, why?

问题描述

如果我使用"inplace = True"(在

If I reset the index of my Pandas dataframe with "inplace=True" (following the documentation) it returns a class 'NoneType'. If I reset the index with "inplace=False" it returns the dataframe with the new index. Why?

print(type(testDataframe))
print(testDataframe.head())

返回:

<class 'pandas.core.frame.DataFrame'>
    ALandbouwBosbouwEnVisserij AantalInkomensontvangers  AantalInwoners  \
0                     73780.0                     None        16979120   
1                       290.0                     None           25243   
2                        20.0                     None            3555   

Set_index返回一个新索引:

Set_index returns a new index:

testDataframe = testDataframe.set_index(['Codering'])
    print(type(testDataframe))
    print(testDataframe.head())

返回

<class 'pandas.core.frame.DataFrame'>
            ALandbouwBosbouwEnVisserij AantalInkomensontvangers  \
Codering                                                          
NL00                           73780.0                     None   
GM1680                           290.0                     None   
WK168000                          20.0                     None   
BU16800000                        15.0                     None   

但是与"inplace = True"相同的set_index:

But the same set_index with "inplace=True":

testDataframe = testDataframe.set_index(['Codering'], inplace=True)
print(type(testDataframe))
print(testDataframe.head())

返回

<class 'NoneType'>
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-50-0d6304ebaae1> in <module>()

版本信息:

python: 3.4.4.final.0
python-bits: 64
pandas: 0.18.1
numpy: 1.11.1
IPython: 5.2.2

推荐答案

好的，现在我明白了，谢谢您的评论！

Ok, now I understand, thanks for the comments!

因此inplace = True应该返回None ，并在原始对象中进行更改.似乎在再次列出数据框时，没有任何更改.

So inplace=True should return None and make the change in the original object. It seemed that on listing the dataframe again, no changes were present.

但是我当然不应该将返回值分配给数据框，即

testDataframe = testDataframe.set_index(['Codering'], inplace=True)

应该是

testDataframe.set_index(['Codering'], inplace=True)

或

testDataframe = testDataframe.set_index(['Codering'], inplace=False)

否则，就地索引更改的返回值(无)是数据帧的新内容，这当然不是预期的.

otherwise the return value of the inplace index change (None) is the new content of the dataframe which is of course not the intend.

我敢肯定，这对许多人来说都是显而易见的，现在对我也是如此，但这并非没有你的帮助，谢谢！！！

I am sure this is obvious to many and now it is to me as well but it wasn't without your help, thanks!!!

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