在第一个熊猫python上排序时，保持第二级的多索引完整

Question

I have sorted my first level of index using the following method : Custom sort order function for groupby pandas python

def my_func(group):
    return sum(group["B"]*group["C"])

idx=df.groupby('A').apply(my_func).reindex(df.index.get_level_values(0))
df.iloc[idx.argsort()]

The issue is that the second level ordering is jumbled up after sorting on the first. How can I make sure that the intra-group order is kept ?

from

A   B C
1 0 1 8
  1 3 3
2 0 1 2
  1 2 2
3 0 1 3
  1 2 4

to

A   B C
2 0 1 2
  1 2 2
3 0 1 3
  1 2 4
1 0 1 8
  1 3 3

and not (last 2 lines inverted)

A   B C
2 0 1 2
  1 2 2
3 0 1 3
  1 2 4
1 1 3 3
  0 1 8

Answer 1

I think you need stable sorting algo - mergesort :

idx=df.index.get_level_values(0).map(df.groupby('A').apply(my_func))
df = df.iloc[idx.argsort(kind='mergesort')]
print (df)
     B  C
A        
2 0  1  2
  1  2  2
3 0  1  3
  1  2  4
1 0  1  8
  1  3  3