title: Adding comma separators to a string in a Dataframe Column with pandas
body: <p><a href="https://i.stack.imgur.com/EEM4l.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/EEM4l.png" alt="Top15.head()"></a></p>
  
  <p>I am trying to add comma separators to indicate thousands to my string to a column in a dataframe. Can someone help with format? I do not understand how to do this to an entire column in a dataframe</p>
  
  <pre><code>Top15['PopEst'] = re.sub("(\d)(?=(\d{3})+(?!\d))", r"\1,", "%d" % Top15['PopEst'])
  </code></pre>