Reorganizing the data in a dataframe

I have data in the following format:

data = 
[
  {'data1': [{'sub_data1': 0}, {'sub_data2': 4}, {'sub_data3': 1}, {'sub_data4': -5}]},
  {'data2': [{'sub_data1': 1}, {'sub_data2': 1}, {'sub_data3': 1}, {'sub_data4': 12}]},
  {'data3': [{'sub_data1': 3}, {'sub_data2': 0}, {'sub_data3': 1}, {'sub_data4': 7}]},

]

How should I reorganize it so that when save it to hdf by

a = pd.DataFrame(data, columns=map(lambda x: x.name, ['data1', 'data2', 'data3']))
a.to_hdf('my_data.hdf')

I get a dataframe in the following format:

            data1       data2     data3
_________________________________________
sub_data1   0           1           1
sub_data2   4           1           0
sub_data3   1           1           1
sub_data4   -5          12          7

update1: after following advice given me below and saving it an hdf file and reading it, I got this which is not what I want:

       data1                        data2                      data3   
0      {u'sub_data1': 22}           {u'sub_data1': 33}          {u'sub_data1': 44}   
1      {u'sub_data2': 0}            {u'sub_data2': 11}          {u'sub_data2': 44}   
2      {u'sub_data3': 12}           {u'sub_data3': 16}          {u'sub_data3': 19}   
3      {u'sub_data4': 0}            {u'sub_data4': 0}           {u'sub_data4': 0}