08-pandas嵌套索引

import numpy as np
import pandas as pd
#1.风格1
df=pd.DataFrame(np.random.rand(4,2),
                columns=["A","B"],
                index=[["1","1","2","2"],
                       ["a","b","a","b"]])
print(df)
#2.风格2
mindex=pd.MultiIndex.from_arrays([["a","a","b","b"],[1,2,1,2]])#双层索引对象
df2=pd.DataFrame(np.random.rand(4,2),
                 columns=(["A","B"]),
                 index=mindex)
print(df2)
#3.风格3
mindex=pd.MultiIndex.from_tuples([("a",1),("a",2),("b",1),("b",2)])#根据元组构建
df3=pd.DataFrame(np.random.rand(4,2),
                 columns=(["A","B"]),
                 index=mindex)
print(df3)
#4.风格4
mindex=pd.MultiIndex.from_product([["a","b"],[1,2]])#根据元组构建
df4=pd.DataFrame(np.random.rand(4,2),
                 columns=(["A","B"]),
                 index=mindex)
print(df4)
#5.风格5
mindex=pd.MultiIndex(levels=[["a","b"],[1,2]],
                     codes=[[0,0,1,1],[0,1,0,1]])#a对应00，b对应11
df4=pd.DataFrame(np.random.rand(4,2),
                 columns=(["A","B"]),
                 index=mindex)
print(df4)
#6.
index=[("beijing",2007),("beijing", 2017),
       ("beijing", 2027),("shenzhen",2007),
       ("shenzhen",2017),("shenzhen",2027)]
money=np.random.rand(6)
Mindex=pd.MultiIndex.from_tuples(index)
city=pd.DataFrame(money,index=Mindex)
print(city)