Pandas: Multilevel column names

Question

pandas has support for multi-level column names:

>>>  x = pd.DataFrame({\'instance\':[\'first\',\'first\',\'first\'],\'foo\':[\'a\',\'b         


        

Answer 1

You can use concat. Give it a dictionary of dataframes where the key is the new column level you want to add.

In [46]: d = {}

In [47]: d['first_level'] = pd.DataFrame(columns=['idx', 'a', 'b', 'c'],
                                         data=[[10, 0.89, 0.98, 0.31],
                                               [20, 0.34, 0.78, 0.34]]).set_index('idx')

In [48]: pd.concat(d, axis=1)
Out[48]:
    first_level
              a     b     c
idx
10         0.89  0.98  0.31
20         0.34  0.78  0.34

You can use the same technique to create multiple levels.

In [49]: d['second_level'] = pd.DataFrame(columns=['idx', 'a', 'b', 'c'],
                                          data=[[10, 0.29, 0.63, 0.99],
                                                [20, 0.23, 0.26, 0.98]]).set_index('idx')

In [50]: pd.concat(d, axis=1)
Out[50]:
    first_level             second_level
              a     b     c            a     b     c
idx
10         0.89  0.98  0.31         0.29  0.63  0.99
20         0.34  0.78  0.34         0.23  0.26  0.98