title: Removing rows if column A and column B have more than one corresponding value in column C
body: <p>I have data with three columns, and I want to remove the row if column A has more than one corresponding value in column B.</p>
  <p>My data:</p>
  <pre><code>   A     B      C
  1  20001 66732  9526
  2  20001 66748  9526
  3  20001 66748  9530
  4  20001 66749  9527
  5  20001 66749  9528
  6  20001 66749  9529
  7  20001 66749  9530
  8  20001 66751  9526
  9  20001 66751  9527
  10 20001 66751  9528
  </code></pre>
  <p>For example, the first row would not be removed, because columns A and B have only one corresponding value in column C. The second and third rows would be removed, because columns A and B have more than one corresponding value in column C. Rows 4-10 would also be removed based on the same condition.</p>
  <p>Is there a more straightforward way of accomplishing this w/o using a loop? Any help would be appreciated.</p>