title: How can I fill empty cells with values from previous rows
body: <p>I have a table that looks like the following example. I'd like to replcae the missing value (if any) in a column with the previous value. So for this table:</p>
  
  <pre><code> col1      col2    
  
   0.1       0.2
   0.23      0.53
    -        0.46
   0.77       - 
     -       0.32
  </code></pre>
  
  <p>I would expect the following results:</p>
  
  <pre><code> col1      col2
  
   0.1       0.2
   0.23      0.53
   0.23      0.46
   0.77      0.46 
   0.77      0.32
  </code></pre>