无法设置 pandas 数据帧的索引 - 获取“KeyError"；
问题描述
我生成了一个如下所示的数据框(summaryDF):
I generate a data frame that looks like this (summaryDF):
accuracy f1 precision recall
0 0.494 0.722433 0.722433 0.722433
0 0.290 0.826087 0.826087 0.826087
0 0.274 0.629630 0.629630 0.629630
0 0.278 0.628571 0.628571 0.628571
0 0.288 0.718750 0.718750 0.718750
0 0.740 0.740000 0.740000 0.740000
0 0.698 0.765133 0.765133 0.765133
0 0.582 0.778547 0.778547 0.778547
0 0.682 0.748235 0.748235 0.748235
0 0.574 0.767918 0.767918 0.767918
0 0.398 0.711656 0.711656 0.711656
0 0.530 0.780083 0.780083 0.780083
因为我知道其中的每一行应该是什么，所以我使用这段代码来设置每一行的名称(这些不是实际的行名，只是为了论证).
Because I know what each row in this should be, I then am using this code to set the names of each row (these aren't the actual row names but just for argument's sake).
summaryDF = summaryDF.set_index(['A','B','C', 'D','E','F','G','H','I','J','K','L'])
但是，我得到:
level = frame[col].values
File "/Users/me/anaconda/lib/python2.7/site-packages/pandas/core/frame.py", line 1797, in __getitem__
return self._getitem_column(key)
File "/Users/me/anaconda/lib/python2.7/site-packages/pandas/core/frame.py", line 1804, in _getitem_column
return self._get_item_cache(key)
File "/Users/me/anaconda/lib/python2.7/site-packages/pandas/core/generic.py", line 1084, in _get_item_cache
values = self._data.get(item)
File "/Users/me/anaconda/lib/python2.7/site-packages/pandas/core/internals.py", line 2851, in get
loc = self.items.get_loc(item)
File "/Users/me/anaconda/lib/python2.7/site-packages/pandas/core/index.py", line 1572, in get_loc
return self._engine.get_loc(_values_from_object(key))
File "pandas/index.pyx", line 134, in pandas.index.IndexEngine.get_loc (pandas/index.c:3824)
File "pandas/index.pyx", line 154, in pandas.index.IndexEngine.get_loc (pandas/index.c:3704)
File "pandas/hashtable.pyx", line 686, in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:12280)
File "pandas/hashtable.pyx", line 694, in pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:12231)
KeyError: 'A'
我不知道自己做错了什么，并且进行了广泛的研究.有什么想法吗?
I have no idea what I am doing wrong and have researched far and wide. Any ideas?
解决方案
我猜你和@jezrael 误解了 pandas 文档中的一个例子:
I guess you and @jezrael misunderstood an example from the pandas docs:
df.set_index(['A', 'B'])
A 和 B 在本例中是列名/标签:
A and B are column names / labels in this example:
In [55]: df = pd.DataFrame(np.random.randint(0, 10, (5,4)), columns=list('ABCD'))
In [56]: df
Out[56]:
A B C D
0 6 9 7 4
1 5 1 3 4
2 4 4 0 5
3 9 0 9 8
4 6 4 5 7
In [57]: df.set_index(['A','B'])
Out[57]:
C D
A B
6 9 7 4
5 1 3 4
4 4 0 5
9 0 9 8
6 4 5 7
文档说应该是列表列标签/数组.
The documentation says it should be list of column labels / arrays.
所以你正在寻找:
In [58]: df.set_index([['A','B','C','D','E']])
Out[58]:
A B C D
A 6 9 7 4
B 5 1 3 4
C 4 4 0 5
D 9 0 9 8
E 6 4 5 7
但正如@jezrael 所建议的那样， df.index = ['A','B',...] 是更快、更惯用的方法...
but as @jezrael has suggested df.index = ['A','B',...] is faster and more idiomatic method...
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