pandas 将多索引的一级拆分为列
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Split one level of an multi index into columns
提问by binnisb
So I have a data frame:
所以我有一个数据框：
df = pd.DataFrame([["foo","fizz",1],["foo","fizz",2],["foo","buzz",3],["foo","buzz",4],["bar","fizz",6],["bar","buzz",8]],columns=["a","b","c"])
a b c
0 foo fizz 1
1 foo fizz 2
2 foo buzz 3
3 foo buzz 4
4 bar fizz 6
5 bar buzz 8
That I can group:
我可以分组：
df2 = df.groupby(["a","b"]).sum()
c
a b
bar buzz 8
fizz 6
foo buzz 7
fizz 3
Which is awesome! But what I really need, instead of the "c" column is two columns, "foo" and "bar":
这太棒了！但我真正需要的是两列，而不是“c”列，“foo”和“bar”：
foo bar
b
buzz 7 8
fizz 3 6
Can someone suggest a way to do this? I tried searching, but I guess I don't have the correct terminology for this so I couldn't find anything.
有人可以建议一种方法吗？我尝试搜索，但我想我没有正确的术语，所以我找不到任何东西。
采纳答案by Anton Protopopov
You could use unstackfor that:
你可以使用unstack：
df2.unstack(level='a')
Example:
例子：
In [146]: df2.unstack(level='a')
Out[146]:
c
a bar foo
b
buzz 8 7
fizz 6 3
After that you'll get multiindexed columns. If you need to get flat dataframe you could use droplevelof multiindex:
之后，您将获得多索引列。如果您需要获得平面数据框，您可以使用droplevel多索引：
df3 = df2.unstack(level='a')
df3.columns = df3.columns.droplevel()
In [177]: df3
Out[177]:
a bar foo
b
buzz 8 7
fizz 6 3
EDIT
编辑
dropleveldrops level from MultiIndex which your columns become after unstack. By default it drops level 0 which is what you need for that dataframe.
droplevel从 MultiIndex 降低您的列在 之后的级别unstack。默认情况下，它会降低级别 0，这是该数据帧所需的级别。
Copy from help(pd.core.index.MultiIndex.droplevel):
复制自help(pd.core.index.MultiIndex.droplevel)：
Help on function droplevelin module pandas.core.index:
droplevel(self, level=0) Return Index with requested level removed. If MultiIndex has only 2 levels, the result will be of Index type not MultiIndex.
Parameters ---------- level : int/level name or list thereof Notes ----- Does not check if result index is unique or not Returns ------- index : Index or MultiIndex
模块 pandas.core.index 中函数droplevel 的帮助：
droplevel(self, level=0) 返回已删除请求级别的索引。如果 MultiIndex 只有 2 个级别，则结果将是 Index 类型而不是 MultiIndex。
Parameters ---------- level : int/level name or list thereof Notes ----- Does not check if result index is unique or not Returns ------- index : Index or MultiIndex
