pandas 分组多索引熊猫数据框
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group multi-index pandas dataframe
提问by silencer
Is it possible to groupby a multi-index (2 levels) pandas dataframe by one of the multi-index levels ?
是否可以按多索引级别之一对多索引（2 级）Pandas数据框进行分组？
The only way I know of doing it is to reset_index on a multiindex and then set index again. I am sure there is a better way to do it, and I want to know how.
我知道这样做的唯一方法是在多索引上重置索引，然后再次设置索引。我相信有更好的方法可以做到这一点，我想知道如何做。
回答by elyase
Yes, use the levelparameter. Take a look here. Example:
是的，使用level参数。看看这里。例子：
In [26]: s
first second third
bar doo one 0.404705
two 0.577046
baz bee one -1.715002
two -1.039268
foo bop one -0.370647
two -1.157892
qux bop one -1.344312
two 0.844885
dtype: float64
In [27]: s.groupby(level=['first','second']).sum()
first second
bar doo 0.981751
baz bee -2.754270
foo bop -1.528539
qux bop -0.499427
dtype: float64
