title: MATLAB drop observations from a timetable not contained in another timetable
body: <p>I have two timetables, each of them have 4 columns, where the first 2 columns are of my particular interest. The first column is a date and the second is an hour.</p>
  
  <p><a href="https://i.stack.imgur.com/pUMPN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pUMPN.png" alt="enter image description here"></a></p>
  
  <p>How can I know which observations (by date an hour) are in the timetable 1 but not in the timetable 2 and, therefore, drop those observations from my timetable 1?</p>
  
  <p>So for example, just by looking I realized that timetable1 included the day 25/05/2015 with hours 1 and 2, but the timetable 2 did not include them, therefore I would like to drop those observations from timetable 1. </p>
  
  <p>I tried using the command <code>groups_timetable1 = findgroups(timetable1.Date,timetable1.Hour);</code>but unfortunately this command does not tell you a lot how to distinguish between observations. </p>
  
  <p>Thank you!</p>