在Pandas中给多层索引降级的方法

import pandas as pd
import numpy as np
df = pd.Data (np.arange(0, 14).reshape(7,2),columns =[\'a\',\'b\'] )
df.a = df.a %3
df[\'who\'] = \'Bob\'
df.loc[df.a%4==0,\'who\'] = \'Alice\'

gp1 = df.groupby(\'who\').agg({\'b\':[sum,np.max, np.min], \'a\':sum})
gp1

#有层次的索引访问方法
gp1.loc[\'Bob\', (\'b\', \'sum\')]

28.0

gp2 = gp1.copy(deep=True)
gp2.columns = gp1.columns.droplevel(0)
gp2

gp3 = gp1.copy(deep=True)
gp3.columns = [\"_\".join(x) for x in gp3.columns.ravel()]
gp3