Python 反转pandas.DataFrame的正确方法？
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Right way to reverse pandas.DataFrame?
提问by Michael
Here is my code:
这是我的代码：
import pandas as pd
data = pd.DataFrame({'Odd':[1,3,5,6,7,9], 'Even':[0,2,4,6,8,10]})
for i in reversed(data):
print(data['Odd'], data['Even'])
When I run this code, i get the following error:
当我运行此代码时，出现以下错误：
Traceback (most recent call last):
File "C:\Python33\lib\site-packages\pandas\core\generic.py", line 665, in _get_item_cache
return cache[item]
KeyError: 5
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "C:\Users\*****\Documents\******\********\****.py", line 5, in <module>
for i in reversed(data):
File "C:\Python33\lib\site-packages\pandas\core\frame.py", line 2003, in __getitem__
return self._get_item_cache(key)
File "C:\Python33\lib\site-packages\pandas\core\generic.py", line 667, in _get_item_cache
values = self._data.get(item)
File "C:\Python33\lib\site-packages\pandas\core\internals.py", line 1656, in get
_, block = self._find_block(item)
File "C:\Python33\lib\site-packages\pandas\core\internals.py", line 1936, in _find_block
self._check_have(item)
File "C:\Python33\lib\site-packages\pandas\core\internals.py", line 1943, in _check_have
raise KeyError('no item named %s' % com.pprint_thing(item))
KeyError: 'no item named 5'
Why am I getting this error?
How can I fix that?
What is the right way to reverse pandas.DataFrame?
为什么我收到这个错误？
我该如何解决？
什么是正确的逆转方法pandas.DataFrame？
采纳答案by behzad.nouri
data.reindex(index=data.index[::-1])
or simply:
或者干脆：
data.iloc[::-1]
will reverse your data frame, if you want to have a forloop which goes from down to up you may do:
将反转您的数据框，如果您想要一个for从下到上的循环，您可以这样做：
for idx in reversed(data.index):
print(idx, data.loc[idx, 'Even'], data.loc[idx, 'Odd'])
or
或者
for idx in reversed(data.index):
print(idx, data.Even[idx], data.Odd[idx])
You are getting an error because reversedfirst calls data.__len__()which returns 6. Then it tries to call data[j - 1]for jin range(6, 0, -1), and the first call would be data[5]; but in pandas dataframe data[5]means column 5, and there is no column 5 so it will throw an exception. ( see docs)
因为你得到一个错误reversed首先调用data.__len__()返回6，然后试图调用data[j - 1]用于j在range(6, 0, -1)和第一个电话会data[5]; 但是在pandas数据框中data[5]表示第5列，并且没有第5列，因此会引发异常。（见文档）
回答by user1951
You can reverse the rows in an even simpler way:
您可以以更简单的方式反转行：
df[::-1]
回答by Michael Styrk
This works:
这有效：
for i,r in data[::-1].iterrows():
print(r['Odd'], r['Even'])
回答by Cybernetic
None of the existing answers resets the index after reversing the dataframe.
在反转数据帧后，现有的答案都不会重置索引。
For this, do the following:
为此，请执行以下操作：
data[::-1].reset_index()
