title: How to Conditionally Set Column Values
body: <p>I would like my code to look at column one first. If it has a valid number for that row, take that value as the COL 3 value. If not, the second option would be to take the value of COL 2 as the value in COL 3. Is there a Function that can do this?  </p>
  
  <pre><code>     COL1  COL2  COL3
  0     1     2
  1    nan    4
  2     3    nan
  3     4     8
  4    nan    10
  5     6    nan
  
       COL3   
  0     1    
  1     4   
  2     3   
  3     4   
  4     10
  5     6
  </code></pre>