pandas学习（五）

pandas学习五

import pandas as pd
import numpy as np

left=pd.DataFrame({
     'key':['a','b','c'],
                  'A':['a1','b1','c1'],
                  'key2':['a3','b3','c3']})
right=pd.DataFrame({
     'key':['a','b','c'],
                  'B':['a2','b2','c2'],
                   'key2':['a3','b3','c3']})

merge合并

pd.merge(left,right,on='key')#类似数据库

	key	A	key2_x	B	key2_y
0	a	a1	a3	a2	a3
1	b	b1	b3	b2	b3
2	c	c1	c3	c2	c3

#how=['left','right','inner','outer'] 类似数据库的四种连接，默认是inner 内连接  indicator可以显示出连接方式
pd.merge(left,right,on=['key','key2'],how='inner',indicator=True)

	key	A	key2	B	_merge
0	a	a1	a3	a2	both
1	b	b1	b3	b2	both
2	c	c1	c3	c2	both

merge index合并

#初始数据
left=pd.DataFrame({
     'key':['a','b','c'],
                  'A':['a1','b1','c1']},index=['k1','k2','k3'])
right=pd.DataFrame({
     'key':['a','b','c'],
                  'A':['a2','b2','c2']},index=['k1','k2','k3'])

pd.merge(left,right,left_index=True,right_index=True,how='outer')

	key_x	A_x	key_y	A_y
k1	a	a1	a	a2
k2	b	b1	b	b2
k3	c	c1	c	c2

pd.merge(left,right,on='key',suffixes=['test1','test2'])

	key	Atest1	Atest2
0	a	a1	a2
1	b	b1	b2
2	c	c1	c2