为什么重命名后我不能访问熊猫中的专栏？[重复]

Question

如果我有一个数据帧并重命名了列，则无法用其新名称访问列。

见示例说明：

import pandas as pd 
df = pd.DataFrame({'a':[1,2], 'b': [10,20]})
df
   a   b
0  1  10
1  2  20
df['a']
0    1
1    2

现在，如果我按照这里建议的方式重命名列“a”。

df.columns.values[0] = 'newname'
df
   newname   b
0        1  10
1        2  20

现在，让我们尝试使用“newname”访问该列

 df['newname']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/gpfs0/export/opt/anaconda-2.3.0/lib/python2.7/site-packages/pandas/core/frame.py", line 1797, in __getitem__
    return self._getitem_column(key)
  File "/gpfs0/export/opt/anaconda-2.3.0/lib/python2.7/site-packages/pandas/core/frame.py", line 1804, in _getitem_column
    return self._get_item_cache(key)
  File "/gpfs0/export/opt/anaconda-2.3.0/lib/python2.7/site-packages/pandas/core/generic.py", line 1084, in _get_item_cache
    values = self._data.get(item)
  File "/gpfs0/export/opt/anaconda-2.3.0/lib/python2.7/site-packages/pandas/core/internals.py", line 2851, in get
    loc = self.items.get_loc(item)
  File "/gpfs0/export/opt/anaconda-2.3.0/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: 'newname'

但我仍然可以使用旧名称访问该列。

df['a']
0    1
1    2
Name: a, dtype: int64

似乎我已经更改了列的名义名称，但这种更改并没有传播到数据帧结构中用于区分列的字典中。

问：为什么会发生这种行为，我如何修复它？

Answer 1

您可以使用以下方法：

In [131]: df.columns = ['newname'] + df.columns.tolist()[1:]

In [132]: df
Out[132]:
   newname   b
0        1  10
1        2  20

或：

In [136]: df = df.rename(columns={df.columns.tolist()[0]:'newname'})

In [137]: df
Out[137]:
   newname   b
0        1  10
1        2  20