title: Populate new column based on existing column checked against regex pandas
body: <p>I have a data frame in Pandas as below</p>
  
  <pre><code>df = pd.DataFrame({'Firstname':['Vishal', 'Nishal', 'Indira', 'Jagdish', 'Tamnna'], 'Actual Age':[25,33,58,58,30]})
  
    Firstname  Actual Age
  0    Vishal          25 
  1   Nishant          33
  2    Indira          58
  3   Jagdish          58   
  4    Tamnna          30
  </code></pre>
  
  <p>and a regex: </p>
  
  <pre><code>\w+ish\w*
  </code></pre>
  
  <p>What I cant seem to figure our is to provide a result as below:</p>
  
  <pre><code>  Firstname  Actual Age  CopyDown
  0    Vishal          25    Vishal
  1   Nishant          33   Nishant
  2    Indira          58   Nishant
  3   Jagdish          58   Jagdish
  4    Tamnna          30   Jagdish
  </code></pre>
  
  <p>So basically what i want to do is look through the Firstname column, and if i can match the regex given, continue copying down that value in a new column until the next match is found, and basically keep doing that until you get to the end.</p>
  
  <p>Any ideas? Ive been stuck on this for days. Its basically a copydown feature i want to implement which might be useful in denormalised datasets. (using dates as stuff)</p>
  
  <p>Thanks in advance</p>