列在数据框中可用，但在切片数据框时不可用

问题描述

在对透视数据帧进行切片时，无法获取列名，并且在下面抛出错误。无法找出正在发生的事情，好像在对数据帧进行切片时未提取可用的列一样。 数据集为“ MovieLens 100K数据集”

数据集为

movieRatings=ratings.pivot_table(index=['user_id'],columns=['title'],values=['rating'])

从“ movieRatings.head（）”中脱颖而出

    rating
title   'Til There Was You (1997)   1-900 (1994)    101 Dalmatians (1996)   12 Angry Men (1957) 187 (1997)  2 Days in the Valley (1996) 20,000 Leagues Under the Sea (1954) 2001: A Space Odyssey (1968)    3 Ninjas: High Noon At Mega Mountain (1998) 39 Steps,The (1935)    ... Yankee Zulu (1994)  Year of the Horse (1997)    You So Crazy (1994) Young Frankenstein (1974)   Young Guns (1988)   Young Guns II (1990)    Young Poisoner's Handbook,The (1995)   Zeus and Roxanne (1997) unknown Á köldum klaka (Cold Fever) (1994)
user_id                                                                                 
1   NaN NaN 2.0 5.0 NaN NaN 3.0 4.0 NaN NaN ... NaN NaN NaN 5.0 3.0 NaN NaN NaN 4.0 NaN
2   NaN NaN NaN NaN NaN NaN NaN NaN 1.0 NaN ... NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN
3   NaN NaN NaN NaN 2.0 NaN NaN NaN NaN NaN ... NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN
4   NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN ... NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN
5   NaN NaN 2.0 NaN NaN NaN NaN 4.0 NaN NaN ... NaN NaN NaN 4.0 NaN NaN NaN NaN 4.0 NaN

下一条语句

starWarsRatings = movieRatings["12 Angry Men (1957)"]
starWarsRatings.head()

错误消息

KeyError                                  Traceback (most recent call last)
D:\Anaconda\lib\site-packages\pandas\core\indexes\base.py in get_loc(self,key,method,tolerance)
   2645             try:
-> 2646                 return self._engine.get_loc(key)
   2647             except KeyError:

pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas\_libs\hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

pandas\_libs\hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

KeyError: '12 Angry Men (1957)'

During handling of the above exception,another exception occurred:

KeyError                                  Traceback (most recent call last)
<ipython-input-134-9c0f30e1dc98> in <module>
----> 1 starWarsRatings = movieRatings["12 Angry Men (1957)"]
      2 starWarsRatings.head()

D:\Anaconda\lib\site-packages\pandas\core\frame.py in __getitem__(self,key)
   2797         if is_single_key:
   2798             if self.columns.nlevels > 1:
-> 2799                 return self._getitem_multilevel(key)
   2800             indexer = self.columns.get_loc(key)
   2801             if is_integer(indexer):

D:\Anaconda\lib\site-packages\pandas\core\frame.py in _getitem_multilevel(self,key)
   2847     def _getitem_multilevel(self,key):
   2848         # self.columns is a MultiIndex
-> 2849         loc = self.columns.get_loc(key)
   2850         if isinstance(loc,(slice,Series,np.ndarray,Index)):
   2851             new_columns = self.columns[loc]

D:\Anaconda\lib\site-packages\pandas\core\indexes\multi.py in get_loc(self,method)
   2660         if not isinstance(key,(tuple,list)):
   2661             # not including list here breaks some indexing,xref #30892
-> 2662             loc = self._get_level_indexer(key,level=0)
   2663             return _maybe_to_slice(loc)
   2664 

D:\Anaconda\lib\site-packages\pandas\core\indexes\multi.py in _get_level_indexer(self,level,indexer)
   2927         else:
   2928 
-> 2929             code = self._get_loc_single_level_index(level_index,key)
   2930 
   2931             if level > 0 or self.lexsort_depth == 0:

D:\Anaconda\lib\site-packages\pandas\core\indexes\multi.py in _get_loc_single_level_index(self,level_index,key)
   2596             return -1
   2597         else:
-> 2598             return level_index.get_loc(key)
   2599 
   2600     def get_loc(self,method=None):

D:\Anaconda\lib\site-packages\pandas\core\indexes\base.py in get_loc(self,tolerance)
   2646                 return self._engine.get_loc(key)
   2647             except KeyError:
-> 2648                 return self._engine.get_loc(self._maybe_cast_indexer(key))
   2649         indexer = self.get_indexer([key],method=method,tolerance=tolerance)
   2650         if indexer.ndim > 1 or indexer.size > 1:

pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas\_libs\index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas\_libs\hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

pandas\_libs\hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

KeyError: '12 Angry Men (1957)'

解决方法

编辑-原始答案不是OP想要的。

问题在于您创建它的方式。数组/列表values参数的解释与简单字符串的解释不同。在这种情况下，您只需要使用字符串one。如果使用数组，则需要使用[ratings，...]进行索引。

所以只需更改表的声明，它就可以工作。

table = df.pivot_table(index=[..],values='JUST A STRING',columns=[..])