title: Replacing values in one column with another based on a 3rd column matching a 4th
body: <p>I'm working with the following example:</p>
  
  <pre><code>Original     Modified     New_Orig     New
  1            2            1            0
  2            4            1            0
  3            6            4            0
  4            8            5            0
  5            10           5            0
  6            12           5            0
  7            14           5            0
  8            16           5            0
  9            18           9            0
  10           20           10           0
  </code></pre>
  
  <p>I want to replace values in <code>New</code> with values from <code>Modified</code> if <code>New_Orig</code> matches with any value in <code>Original</code>.</p>
  
  <p>Ideally <code>New</code> will look like this:</p>
  
  <pre><code>New
  2  
  2
  8
  10
  10
  10
  10
  10
  18
  20  
  </code></pre>
  
  <p>Any help much appreciated.</p>
  
  <p>Kind regards,</p>