title: Drop Repeated Values in Column, Retaining the Row
body: <p>I have a problem similar to dropping duplicates, but I need to retain the row that has the repeated value.  So essentially, I need to retain the first value and then replace every repetition of it with ''.  </p>
  
  <pre><code>Col1    Col2
  a        1
  b        1
  c        1
  d        2
  </code></pre>
  
  <p>What I need is:</p>
  
  <pre><code>Col1     Col2 
  a        1
  b
  c
  d        2
  </code></pre>
  
  <p>Thanks.</p>