使用
merge，默认情况下是内部联接：
pd.merge(df1, df2, left_index=True, right_index=True)
或
join，默认情况下为左连接：
df1.join(df2)
或
concat，默认情况下为外部联接：
pd.concat([df1, df2], axis=1)
样品 ：
df1 = pd.Dataframe({'a':range(6), 'b':[5,3,6,9,2,4]}, index=list('abcdef'))print (df1) a ba 0 5b 1 3c 2 6d 3 9e 4 2f 5 4df2 = pd.Dataframe({'c':range(4), 'd':[10,20,30, 40]}, index=list('abhi'))print (df2) c da 0 10b 1 20h 2 30i 3 40#default inner joindf3 = pd.merge(df1, df2, left_index=True, right_index=True)print (df3) a b c da 0 5 0 10b 1 3 1 20#default left joindf4 = df1.join(df2)print (df4) a b c da 0 5 0.0 10.0b 1 3 1.0 20.0c 2 6 NaN NaNd 3 9 NaN NaNe 4 2 NaN NaNf 5 4 NaN NaN#default outer joindf5 = pd.concat([df1, df2], axis=1)print (df5) a b c da 0.0 5.0 0.0 10.0b 1.0 3.0 1.0 20.0c 2.0 6.0 NaN NaNd 3.0 9.0 NaN NaNe 4.0 2.0 NaN NaNf 5.0 4.0 NaN NaNh NaN NaN 2.0 30.0i NaN NaN 3.0 40.0
