python 数据合并函数merge( )_Pandas的数据拼接-merge函数

27. Pandas的数据拼接-merge函数

concat函数可以实现内外连接，而pandas的merge函数可以真正实现数据库的内外连接，且外连接还可以有左右连接的特性。

merge函数默认拼接数据是inner join即内连接。下面以学生选课为例，设计两个DataFrame通过merge函数来拼接合并。

import pandas as pd

import numpy as np

col1 = "class_name class_id class_lecturer".split()

col2 = "class_id stu_id".split()

val1 = [["IT", 100, "Wangli"],["CS", 101, "WangMa"],["CAD", 102, "Liping"]]

val2 = [[100, 20181115],[100, 20181116],[101, 20181117]]

course = pd.DataFrame(val1, columns = col1)

print "***course", "*" * 38

print course

choose = pd.DataFrame(val2, columns = col2)

print "***choose", "*" * 38

print choose

print "***course merge choose", "*" * 25

print course.merge(choose)

print "***choose merge course", "*" * 25

print choose.merge(course)

程序的执行结果：

***course **************************************

class_name class_id class_lecturer

0 IT 100 Wangli

1 CS 101 WangMa

2 CAD 102 Liping

***choose **************************************

class_id stu_id

0 100 20181115

1 100 20181116

2 101 20181117

***course merge choose *************************

class_name class_id class_lecturer stu_id

0 IT 100 Wangli 20181115

1 IT 100 Wangli 20181116

2 CS 101 WangMa 20181117

***choose merge cours