title: How to select specific ID from a csv file?
body: <p>I have 2 csv file, one containing all my users with their id, and another with all the trips that users has made. 
  I want to select only the user that has made a trip. So I need to extract from the user list, only the one who have the same id on the list of the trip in the column user id.
  Have you got an idea to do this ?
  Thank you</p>