title: how to extract duplicate data in csv file
body: <p>I'm working on modeling users opinions on YouTube, so I extracted a huge amounts of data (comments and videos), I have a csv file with 5 columns(channelId, videoId, userId, date of comment and polarity) and nearly 80k rows. Now I need to collect each user's comments separately in csv file.
  How can I extract the all comments for each userId?? I tried to extract duplicates but it doesn't work.
  Can anyone help me with a little python script?</p>