title: How to fill missing values using last available data from past months?
body: <p>I have a dataframe like this:   </p>
  
  <pre><code>Month/Year  Value   
  01/2018     100 
  03/2018     200 
  06/2018     500 
  </code></pre>
  
  <p>The values for 02/2018, 04/2018 and 05/2018 is missing because the value did not change in those months. I would like to have a dataframe which incudes the missing months: </p>
  
  <pre><code>Month/Year  Value   
  01/2018     100 
  02/2018     100 
  03/2018     200 
  04/2018     200 
  04/2018     200 
  06/2018     500 
  </code></pre>
  
  <p>Can anyone help?</p>