如何在python熊猫中找到带有多索引的至少两个数据框列？

Question

I have got two pandas Dataframes df1 and df2 . df1 has a multi-index:

                  A   
instance index
a        0        10 
         1        11  
         2        7
b        0        8
         1        9
         2        13

The frame df2 has the same first-level index as df1 :

              B   
instance 
a             5 
b             12

I want to do two things:

1) Assign the values in df2 to the all the rows of df1

                  A    B
instance index
a        0        10   5
         1        11   5
         2        7    5
b        0        8    12
         1        9    12
         2        13   12

2) Create a dataframe object that represents the minimum of values in A and B without concatenating the two dataframes like above:

min(df1,df2):
                  min   
instance index
a        0        5   
         1        5   
         2        5   
b        0        8    
         1        9    
         2        12   

Answer 1

For your first request, you can use DataFrame.join :

>>> df1.join(df2)
                 A   B
instance index        
a        0      10   5
         1      11   5
         2       7   5
b        0       8  12
         1       9  12
         2      13  12

For your second, you can simply call min(axis=1) on that object:

>>> df1.join(df2).min(axis=1).to_frame("min")
                min
instance index     
a        0        5
         1        5
         2        5
b        0        8
         1        9
         2       12