从另一个 df 引用提取相应的 df 值

Question

There are 2 dataframes with 1 to 1 correspondence. I can retrieve an idxmax from all columns in df1 .

Input:

df1 = pd.DataFrame({'ref':[2,4,6,8,10,12,14],'value1':[76,23,43,34,0,78,34],'value2':[1,45,8,0,76,45,56]})
df2 = pd.DataFrame({'ref':[2,4,6,8,10,12,14],'value1_pair':[0,0,0,0,180,180,90],'value2_pair':[0,0,0,0,90,180,90]})

df=df1.loc[df1.iloc[:,1:].idxmax(), 'ref']

Output: df1, df2 and df

     ref  value1  value2
0    2      76       1
1    4      23      45
2    6      43       8
3    8      34       0
4   10       0      76
5   12      78      45
6   14      34      56  

     ref  value1_pair  value2_pair
0    2            0            0
1    4            0            0
2    6            0            0
3    8            0            0
4   10          180           90
5   12          180          180
6   14           90           90

    5    12
    4    10
Name: ref, dtype: int64

Now I want to create a df which contains 3 columns

Desired Output df :

ref   max value   corresponding value
12    78          180
10    76          90

What are the best options to extract the corresponding values from df2 ?

Answer 1

Your main problem is matching the columns between df1 and df2 . Let's rename them properly, melt both dataframes, merge and extract:

(df1.melt('ref')
    .merge(df2.rename(columns={'value1_pair':'value1', 
                               'value2_pair':'value2'})
              .melt('ref'), 
           on=['ref', 'variable'])
    .sort_values('value_x')
    .groupby('variable').last()
)

Output:

          ref  value_x  value_y
variable                       
value1     12       78      180
value2     10       76       90