title: Modify row in DataTable based on two columns that are identical
body: <p>I have data like so:</p>
  
  <pre><code>Col 1 | Col 2
  -------------
    a   |   9
    b   |   2
    a   |   9
    c   |   3
  </code></pre>
  
  <p>I need to remove the 9 from any duplicates of a without removing the row and keeping column 1. I added my entire DataTable to a Dictionary and was going to modify that and readd it to a new DataTable but this seems to inefficient. What's the most efficient way to do this?</p>