title: Remove duplicate rows by considering two columns and ignore the order
body: <p>I have a dataframe with three columns. Column 1, Column 2 and third column is Value. Data frame is sorted according to the value (desc). In the below case, I want to remove third row because A>B is already there, so I don't want to consider B>A. How can I remove third column (such instances). This applies to all, for example, A>C is already present, so C>A should be removed.</p>
  
  <pre><code>Column1 Column2 Value
  A       B       10
  A       C       8
  B       A       6
  </code></pre>