Pandas: Calculate Median of Group over Columns

Question

Given the following data frame:

import pandas as pd

df = pd.DataFrame({\'COL1\': [\'A\', \'A\',\'A\',\'A\',\'B\',\'B\'], 
                   \'COL2\' : [\'A         


        

Answer 1

You already had the idea -- groupby COL1 and COL2 and calculate median.

m = df.groupby(['COL1', 'COL2'])[['COL3','COL4']].apply(np.median)
m.name = 'MEDIAN'

print df.join(m, on=['COL1', 'COL2'])

  COL1 COL2  COL3  COL4  MEDIAN
0    A   AA     2     0     1.5
1    A   AA     3     1     1.5
2    A   BB     4     2     3.5
3    A   BB     5     3     3.5
4    B   BB     4     4     3.0
5    B   BB     2     2     3.0