pandas入门——数据合并merge函数

数据合并merge函数

# 导入pandas和numpy包
import pandas as pd
import numpy as np

# 创建两个数据框
df_left = pd.DataFrame(data=np.ones((5,6)),columns=["a","b","c","d","e","f"],index=["k1","k2","k3","k4","k5"])
df_right = pd.DataFrame(data=np.ones((5,6))*2,columns=["e","f","g","h","j","k"],index=["k3","k4","k5","k6","k7"])

df_left["key1"] = ["k1","k0","k0","k1","k1"]
df_left["key2"] = ["k0","k0","k1","k1","k0"]

df_right["key1"] = ["k1","k0","k0","k0","k1"]
df_right["key2"] = ["k0","k1","k1","k1","k0"]

print(df_r
4000
ight)
print(df_left)

e   f   g   h   j   k   key1    key2
k3  2.0 2.0 2.0 2.0 2.0 2.0 k1  k0
k4  2.0 2.0 2.0 2.0 2.0 2.0 k0  k1
k5  2.0 2.0 2.0 2.0 2.0 2.0 k0  k1
k6  2.0 2.0 2.0 2.0 2.0 2.0 k0  k1
k7  2.0 2.0 2.0 2.0 2.0 2.0 k1  k0

a   b   c   d   e   f   key1    key2
k1  1.0 1.0 1.0 1.0 1.0 1.0 k1  k0
k2  1.0 1.0 1.0 1.0 1.0 1.0 k0  k0
k3  1.0 1.0 1.0 1.0 1.0 1.0 k0  k1
k4  1.0 1.0 1.0 1.0 1.0 1.0 k1  k1
k5  1.0 1.0 1.0 1.0 1.0 1.0 k1  k0

print(pd.merge(left=df_left,right=df_right,on=["key1","key2"],how="inner"))

a   b   c   d   e_x f_x key1    key2    e_y f_y g   h   j   k
0   1.0 1.0 1.0 1.0 1.0 1.0 k1  k0  2.0 2.0 2.0 2.0 2.0 2.0
1   1.0 1.0 1.0 1.0 1.0 1.0 k1  k0  2.0 2.0 2.0 2.0 2.0 2.0
2   1.0 1.0 1.0 1.0 1.0 1.0 k1  k0  2.0 2.0 2.0 2.0 2.0 2.0
3   1.0 1.0 1.0 1.0 1.0 1.0 k1  k0  2.0 2.0 2.0 2.0 2.0 2.0
4   1.0 1.0 1.0 1.0 1.0 1.0 k0  k1  2.0 2.0 2.0 2.0 2.0 2.0
5   1.0 1.0 1.0 1.0 1.0 1.0 k0  k1  2.0 2.0 2.0 2.0 2.0 2.0
6   1.0 1.0 1.0 1.0 1.0 1.0 k0  k1  2.0 2.0 2.0 2.0 2.0 2.0

pd.merge(left=df_left,right=df_right,on=["key1","key2"],how="outer",indicator=True)

a   b   c   d   e_x f_x key1    key2    e_y f_y g   h   j   k   _merge
0   1.0 1.0 1.0 1.0 1.0 1.0 k1  k0  2.0 2.0 2.0 2.0 2.0 2.0 both
1   1.0 1.0 1.0 1.0 1.0 1.0 k1  k0  2.0 2.0 2.0 2.0 2.0 2.0 both
2   1.0 1.0 1.0 1.0 1.0 1.0 k1  k0  2.0 2.0 2.0 2.0 2.0 2.0 both
3   1.0 1.0 1.0 1.0 1.0 1.0 k1  k0  2.0 2.0 2.0 2.0 2.0 2.0 both
4   1.0 1.0 1.0 1.0 1.0 1.0 k0  k0  NaN NaN NaN NaN NaN NaN left_only
5   1.0 1.0 1.0 1.0 1.0 1.0 k0  k1  2.0 2.0 2.0 2.0 2.0 2.0 both
6   1.0 1.0 1.0 1.0 1.0 1.0 k0  k1  2.0 2.0 2.0 2.0 2.0 2.0 both
7   1.0 1.0 1.0 1.0 1.0 1.0 k0  k1  2.0 2.0 2.0 2.0 2.0 2.0 both
8   1.0 1.0 1.0 1.0 1.0 1.0 k1  k1  NaN NaN NaN NaN NaN NaN left_only

pd.merge(left=df_left,right=df_right,on=["key1","key2"],how="left",left_index=True,right_index=True,indicator=True)

a   b   c   d   e_x f_x key1    key2    e_y f_y g   h   j   k   _merge
k1  1.0 1.0 1.0 1.0 1.0 1.0 k1  k0  NaN NaN NaN NaN NaN NaN left_only
k2  1.0 1.0 1.0 1.0 1.0 1.0 k0  k0  NaN NaN NaN NaN NaN NaN left_only
k3  1.0 1.0 1.0 1.0 1.0 1.0 k0  k1  2.0 2.0 2.0 2.0 2.0 2.0 both
k4  1.0 1.0 1.0 1.0 1.0 1.0 k1  k1  2.0 2.0 2.0 2.0 2.0 2.0 both
k5  1.0 1.0 1.0 1.0 1.0 1.0 k1  k0  2.0 2.0 2.0 2.0 2.0 2.0 both

pd.merge(left=df_left,right=df_right,on=["key1","key2"],how="right",left_index=True,right_index=True,indicator=True,suffixes=("_left","_right"))

a   b   c   d   e_left  f_left  key1    key2    e_right f_right g   h   j   k   _merge
k3  1.0 1.0 1.0 1.0 1.0 1.0 k0  k1  2.0 2.0 2.0 2.0 2.0 2.0 both
k4  1.0 1.0 1.0 1.0 1.0 1.0 k1  k1  2.0 2.0 2.0 2.0 2.0 2.0 both
k5  1.0 1.0 1.0 1.0 1.0 1.0 k1  k0  2.0 2.0 2.0 2.0 2.0 2.0 both
k6  NaN NaN NaN NaN NaN NaN NaN NaN 2.0 2.0 2.0 2.0 2.0 2.0 right_only
k7  NaN NaN NaN NaN NaN NaN NaN NaN 2.0 2.0 2.0 2.0 2.0 2.0 right_only