import pandas as pd
import numpy as np
url = 'https://raw.githubusercontent.com/HoijanLai/dataset/master/PoliceKillingsUS.csv'
df = pd.read_csv(url,sep=',')
df

1.对多列运算

df.groupby('race').agg({'age':np.median,'signs_of_mental_illness':np.sum})

2.对单列进行多个运算

df.groupby('flee')['age'].agg([np.mean,np.median])