title: Duplicates using python, if any create a new column when there's a match
body: <p>I'm currently trying to conduct an analysis where people might be doing something to avoid the system. So, I created a new field inside my dataFrame where I appended the Issue Date and the Name of the potential offender. What I want is: if any of the rows have the same Audit ID, say yes, if not, NaN.</p>
  <p>So for example, I have:</p>
  <pre><code>Offender Name  Issue Date  Audit ID
  Joe            12/02/2020  Joe-12/02/20
  Nic            20/02/2020  Nic-20/02/20
  Mat            01/02/2020  Mat-01/02/20
  Joe            12/02/2020  Joe-12/02/20
  </code></pre>
  <p>And I want something like:</p>
  <pre><code>Offender Name  Issue Date  Audit ID        Matches
  Joe            12/02/2020  Joe-12/02/20    Yes
  Nic            20/02/2020  Nic-20/02/20    No
  Mat            01/02/2020  Mat-01/02/20    No 
  Joe            12/02/2020  Joe-12/02/20    Yes
  </code></pre>
  <p>I'd appreciate any insights anyone can give me</p>