title: Count the repetition in a column in pandas
body: <p>I have a column which has the ticketID for a show,(each family member uses the same ticketID ) i want to create a new cloumn which is family size by counting how many times the ticketID is repeated.</p>
  
  <pre><code>ticketID
  113796
  2543
  19950
  382653
  349211
  3101297
  PC 17562
  113503
  113503
  </code></pre>