问题:正确的方法来反转pandas.DataFrame?

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'])

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'

为什么会出现此错误?
我该如何解决?
正确的逆转方法是pandas.DataFrame什么?

Here is my code:

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:

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?


回答 0

data.reindex(index=data.index[::-1])

或者简单地:

data.iloc[::-1]

将反转您的数据帧,如果您想使for循环从下到上,则可以执行以下操作:

for idx in reversed(data.index):
    print(idx, data.loc[idx, 'Even'], data.loc[idx, 'Odd'])

要么

for idx in reversed(data.index):
    print(idx, data.Even[idx], data.Odd[idx])

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jrange(6, 0, -1)和第一个电话会data[5]; 但在pandas数据框中data[5]表示第5列,没有第5列,因此它将引发异常。(请参阅文档

data.reindex(index=data.index[::-1])

or simply:

data.iloc[::-1]

will reverse your data frame, if you want to have a for loop which goes from down to up you may do:

for idx in reversed(data.index):
    print(idx, data.loc[idx, 'Even'], data.loc[idx, 'Odd'])

or

for idx in reversed(data.index):
    print(idx, data.Even[idx], data.Odd[idx])

You are getting an error because reversed first calls data.__len__() which returns 6. Then it tries to call data[j - 1] for j in 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 )


回答 1

您可以以更简单的方式反转行:

df[::-1]

You can reverse the rows in an even simpler way:

df[::-1]

回答 2

反转数据帧后,现有答案都不会重置索引。

为此,请执行以下操作:

 data[::-1].reset_index()

这是一个实用程序函数,它也按照@Tim的注释删除了旧的索引列:

def reset_my_index(df):
  res = df[::-1].reset_index(drop=True)
  return(res)

只需将数据框传递给函数

None of the existing answers resets the index after reversing the dataframe.

For this, do the following:

 data[::-1].reset_index()

Here’s a utility function that also removes the old index column, as per @Tim’s comment:

def reset_my_index(df):
  res = df[::-1].reset_index(drop=True)
  return(res)

Simply pass your dataframe into the function


回答 3

这有效:

    for i,r in data[::-1].iterrows():
        print(r['Odd'], r['Even'])

This works:

    for i,r in data[::-1].iterrows():
        print(r['Odd'], r['Even'])

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