title: Print Column contents, according to particular contents of another column
body: <p>I have a DataFrame with columns like trip_id, service_id etc., like</p>
  
  <pre><code>trip_id     service_id
  1            weekday
  2            weekday
  3            weekday
  4            saturday
  5            saturday
  6            holiday
  7            sunday
  </code></pre>
  
  <p>I want to print out the trip_id's for all 'weekday', for all saturdays and holidays, separately. I tried with the </p>
  
  <pre><code>join_df.query(join_df['service_id'] == 'weekday')
  </code></pre>
  
  <p>way, but it doesn't seem to be the right one. I also tried </p>
  
  <pre><code>print join_df[join_df.service_id =='weekdays']
  </code></pre>
  
  <p>didnt work. Got an empty dataframe as the output.</p>
  
  <p>Could anybody help me with this please.
  Thank you</p>