连接两个panda数据帧

import pandas as pd

# 创建两个数据帧
df1 = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]})
df2 = pd.DataFrame({'A': [7, 8, 9], 'B': [10, 11, 12]})

# 按行连接
result = pd.concat([df1, df2], axis=0)

# 按列连接
result = pd.concat([df1, df2], axis=1)

import pandas as pd

# 创建两个数据帧
df1 = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6], 'key': ['K1', 'K2', 'K3']})
df2 = pd.DataFrame({'C': [7, 8, 9], 'D': [10, 11, 12], 'key': ['K1', 'K2', 'K4']})

# 根据key列进行连接
result = pd.merge(df1, df2, on='key')

# 内连接
result = pd.merge(df1, df2, on='key', how='inner')

import pandas as pd

# 创建两个数据帧
df1 = pd.DataFrame({'A': [1, 2, 3], 'B': [4, 5, 6]}, index=['K1', 'K2', 'K3'])
df2 = pd.DataFrame({'C': [7, 8, 9], 'D': [10, 11, 12]}, index=['K1', 'K2', 'K4'])

# 根据索引进行连接
result = df1.join(df2)

# 左连接
result = df1.join(df2, how='left')