Python Pandas Pivot - 为什么失败
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Python Pandas Pivot - Why Fails
提问by user1617979
I have tried for a while to get this to wrk and I can't - I read the documentation and I must be misunderstanding something
我已经尝试了一段时间来解决这个问题，但我不能 - 我阅读了文档，我一定是误解了一些东西
I have a Data Frame in long format and I want to make it wide - this is quite common. But I get an error
我有一个长格式的数据框，我想让它变宽 - 这很常见。但我收到一个错误
from pandas import DataFrame
data = DataFrame({'value' : [1,2,3,4,5,6,7,8,9,10,11,12],
'group' : ['a','a','a','b','b','b','b','c','c','c','d','d']})
data.pivot(columns='group')
the error I get is (the lats part, as they are quite extensive): ValueError: cannot label index with a null key
我得到的错误是（lats 部分，因为它们非常广泛）：ValueError: cannot label index with a null key
I tried this in python (notebook) and also on regular python c command line in OS X with the same result
我在 python (notebook) 和 OS X 中的常规 python c 命令行中尝试过这个，结果相同
Thanks for any insight, I am sure it will be something basic
感谢您的任何见解，我相信这将是一些基本的东西
回答by Anzel
From what you were trying to do, you were trying to pass 'group' as indexso the pivot fails.
It should be:
从您尝试做的事情来看，您试图通过“组”，index因此支点失败。它应该是：
data.pivot(data.index, 'group')
or,
或者，
# the format is pivot(index=None, columns=None, values=None)
data.pivot(index=data.index, columns='group')
However I'm not entirely sure what expected output you want, if you just want shorter presentation, you can always use transpose:
但是我不完全确定你想要什么预期的输出，如果你只是想要更短的演示，你总是可以使用transpose：
data.T
or, the best for presentation in your case, is groupby:
或者，在您的案例中最适合展示的是groupby：
data.groupby('group').sum()
value
group
a 6
b 22
c 27
d 23
