title: Flatten nested pandas dataframe
body: <p>I'm wondering how to flatten the nested pandas dataframe as demonstrated in the picture attached. <a href="https://i.stack.imgur.com/7UR1f.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7UR1f.jpg" alt="enter image description here"></a></p>
  
  <p>The nested attribute is given by 'data' field. In short: I have a list of participants (denoted by 'participant_id') and they submitted responses ('data') at different times. I need to create the wide dataframe, where for each participant at each time stamp there is a row of records of their data ('q1', 'q2',...,'summary')</p>
  
  <p>Many thanks in advance!</p>