Python 无法设置 Pandas 数据框的索引 - 获取“KeyError”
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Can't set index of a pandas data frame - getting "KeyError"
提问by Dhruv Ghulati
I generate a data frame that looks like this (summaryDF):
我生成了一个如下所示的数据框 ( 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
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).
因为我知道这里面的每一行应该是什么，然后我使用这个代码来设置每一行的名称（这些不是实际的行名称，只是为了参数）。
summaryDF = summaryDF.set_index(['A','B','C', 'D','E','F','G','H','I','J','K','L'])
However, I am getting:
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'
I have no idea what I am doing wrong and have researched far and wide. Any ideas?
我不知道我做错了什么，并且进行了广泛的研究。有任何想法吗？
采纳答案by MaxU
I guess you and @jezrael misunderstood an example from the pandas docs:
我猜你和@jezrael 误解了熊猫文档中的一个例子：
df.set_index(['A', 'B'])
Aand Bare column names / labels in this example:
A和B是本例中的列名/标签：
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
The documentationsays it should be listof column labels / arrays.
该文件说，它应该是列表的列标签/的阵列。
so you were looking for:
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
but as @jezrael has suggested df.index = ['A','B',...]is faster and more idiomatic method...
但正如@jezrael 所建议的那样df.index = ['A','B',...]是更快、更惯用的方法......
回答by jezrael
You need assign listto summaryDF.index, if lengthof listis same as lengthof DataFrame:
您需要分配list给summaryDF.index，如果lengthoflist与lengthof相同DataFrame：
summaryDF.index = ['A','B','C', 'D','E','F','G','H','I','J','K','L']
print (summaryDF)
accuracy f1 precision recall
A 0.494 0.722433 0.722433 0.722433
B 0.290 0.826087 0.826087 0.826087
C 0.274 0.629630 0.629630 0.629630
D 0.278 0.628571 0.628571 0.628571
E 0.288 0.718750 0.718750 0.718750
F 0.740 0.740000 0.740000 0.740000
G 0.698 0.765133 0.765133 0.765133
H 0.582 0.778547 0.778547 0.778547
I 0.682 0.748235 0.748235 0.748235
J 0.574 0.767918 0.767918 0.767918
K 0.398 0.711656 0.711656 0.711656
L 0.530 0.780083 0.780083 0.780083
print (summaryDF.index)
Index(['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L'], dtype='object')
Timings:
时间：
In [117]: %timeit summaryDF.index = ['A','B','C', 'D','E','F','G','H','I','J','K','L']
The slowest run took 6.86 times longer than the fastest. This could mean that an intermediate result is being cached.
10000 loops, best of 3: 76.2 μs per loop
In [118]: %timeit summaryDF.set_index(pd.Index(['A','B','C', 'D','E','F','G','H','I','J','K','L']))
The slowest run took 6.77 times longer than the fastest. This could mean that an intermediate result is being cached.
1000 loops, best of 3: 227 μs per loop
Another solution is convert listto numpy array:
另一种解决方案是转换list为numpy array：
summaryDF.set_index(np.array(['A','B','C', 'D','E','F','G','H','I','J','K','L']), inplace=True)
print (summaryDF)
accuracy f1 precision recall
A 0.494 0.722433 0.722433 0.722433
B 0.290 0.826087 0.826087 0.826087
C 0.274 0.629630 0.629630 0.629630
D 0.278 0.628571 0.628571 0.628571
E 0.288 0.718750 0.718750 0.718750
F 0.740 0.740000 0.740000 0.740000
G 0.698 0.765133 0.765133 0.765133
H 0.582 0.778547 0.778547 0.778547
I 0.682 0.748235 0.748235 0.748235
J 0.574 0.767918 0.767918 0.767918
K 0.398 0.711656 0.711656 0.711656
L 0.530 0.780083 0.780083 0.780083
