title: Pandas dataframe multiple groupby filtering
body: <p>I have the following dataframe:</p>
  
  <pre><code>df2 = pd.DataFrame({'season':[1,1,1,2,2,2,3,3],'value' : [-2, 3,1,5,8,6,7,5], 'test':[3,2,6,8,7,4,25,2],'test2':[4,5,7,8,9,10,11,12]},index=['2020', '2020', '2020','2020', '2020', '2021', '2021', '2021']) 
  df2.index=  pd.to_datetime(df2.index)  
  df2.index = df2.index.year
  print(df2)
  
          season  test  test2  value
  2020       1     3      4     -2
  2020       1     2      5      3
  2020       1     6      7      1
  2020       2     8      8      5
  2020       2     7      9      8
  2021       2     4     10      6
  2021       3    25     11      7
  2021       3     2     12      5
  </code></pre>
  
  <p>I would like to filter it to obtain for each year and each season of that year the maximum value of the column 'value'. How can I do that efficiently?</p>
  
  <p>Expected result:</p>
  
  <pre><code>print(df_result)
  
          season  value  test  test2
  year                            
  2020       1      3     2      5
  2020       2      8     7      9
  2021       2      6     4     10
  2021       3      7     25    11
  </code></pre>
  
  <p>Thank you for your help,</p>
  
  <p>Pierre</p>