Question

我解析了大量的xml文件以获得一个pandas数据框。我现在需要删除一些列以进行数据分析。我无法在先前的问题中找到确切的错误。我用过-

data = data["Rig Mode","Bit on Bottom","Block Position","Block Velocity",..]

并收到一条错误消息（完整的错误消息在帖子结尾）-

KeyError: 'Key length (22) exceeds index depth (2)'

因此，我研究并转到了this post，其中提到了与lexsort depth相关的错误，而我的错误恰恰如上所述。我根据上面的帖子对索引进行了排序-

`data = data.sort_index(level=1)`
 pd.__version__
 '0.22.0' 
 Python version - 3.6.4

并得到完全相同的错误。在下面，我获取了我的多索引详细信息-

data.columns

#MultiIndex(levels=[['Bit on Bottom','Block Position', 'Block Velocity',  'Rig Mode',...], ['', '1/min', 'L/min', 'dega', ...]],
           labels=[[38, 0, 2, 22, ...]],
           names=['Description', 'Unit'])

这是我在准备数据帧时构建多索引的方式，现在将列标题解析为数据集中的行-

data.columns = pd.MultiIndex.from_arrays([data.iloc[0],data.iloc[1]], names = ['Description','Unit'])
data=data.iloc[2:]

#### complete error message: 

>     --------------------------------------------------------------------------- KeyError                                  Traceback (most recent call
> last) <ipython-input-119-60ad57c2383f> in <module>()
>       3                               "Continuous Survey Depth","Pump 1 Stroke Rate","Pump 2 Stroke Rate","Pump 3 Stroke Rate",
>       4                               "Average Standpipe Pressure","Slips stat (1=Out,0=In)", "Weight on Bit","Mud Flow
> In","Time","Average Surface Torque",
> ----> 5                               "MWD Turbine RPM"]
> 
> ~\Anaconda3\lib\site-packages\pandas\core\frame.py in
> __getitem__(self, key)    2135             return self._getitem_frame(key)    2136         elif is_mi_columns:
> -> 2137             return self._getitem_multilevel(key)    2138         else:    2139             return self._getitem_column(key)
> 
> ~\Anaconda3\lib\site-packages\pandas\core\frame.py in
> _getitem_multilevel(self, key)    2179     2180     def _getitem_multilevel(self, key):
> -> 2181         loc = self.columns.get_loc(key)    2182         if isinstance(loc, (slice, Series, np.ndarray, Index)):    2183          
> new_columns = self.columns[loc]
> 
> ~\Anaconda3\lib\site-packages\pandas\core\indexes\multi.py in
> get_loc(self, key, method)    2076         if self.nlevels < keylen:  
> 2077             raise KeyError('Key length ({0}) exceeds index depth
> ({1})'
> -> 2078                            ''.format(keylen, self.nlevels))    2079     2080         if keylen == self.nlevels and self.is_unique:
> 
> KeyError: 'Key length (22) exceeds index depth (2)'

Answer 1

要选择列的子集，必须使用[[ ]]：

data = data[["Rig Mode","Bit on Bottom","Block Position","Block Velocity",..]]

__getindex__重载了很多。

In [11]: df = pd.DataFrame([[1, 2], [3, 4], [5, 6]], columns=["A", "B"])

In [12]: df
Out[12]:
   A  B
0  1  2
1  3  4
2  5  6

In [13]: df["A"]
Out[13]:
0    1
1    3
2    5
Name: A, dtype: int64

In [14]: df["A", "B"]
KeyError: ('A', 'B')

使用MultiIndex尝试选择列：

In [21]: df = pd.DataFrame([[1, 2], [3, 4], [5, 6]], columns=[["A", "AA"], ["B", "BB"]])

In [22]: df
Out[22]:
   A AA
   B BB
0  1  2
1  3  4
2  5  6

In [23]: df["A"]
Out[23]:
   B
0  1
1  3
2  5

In [24]: df["A", "B"]
Out[24]:
0    1
1    3
2    5
Name: (A, B), dtype: int64

KeyError：键长度超过索引深度-Pandas MultiIndex

1 个答案: