知识问答

正确的方法来反转pandas.DataFrame？

内容 隐藏
问题：正确的方法来反转pandas.DataFrame？
回答 0
回答 1
回答 2
回答 3

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？

点击查看英文原文

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j在range(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）

点击查看英文原文 
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]
点击查看英文原文

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

点击查看英文原文

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'])
点击查看英文原文

This works:

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