title: Getting rid of combinations of IDs already present in the data
body: <p>I have the following dataset</p>
  <pre><code>idA idB value
  1   5   0.11
  2   6   0.25
  3   7   0.3
  4   8   0.4
  .   .   .
  .   .   .
  .   .   .
  .   .   .
  .   .   .
  5   1   0.11
  6   2   0.25
  7   3   0.3
  8   4   0.4
  </code></pre>
  <p>idA and idB are IDs for the same dataset (basically both idA and idB come from the same column).
  So, if I have (idA = 1, idB = 5) it's the same as (idB = 1, idA = 5).
  I want to get rid of the multiple cases (the one at the botom in my df), in order to obtain</p>
  <pre><code>idA idB value
  1   5   0.11
  2   6   0.25
  3   7   0.3
  4   8   0.4
  .   .   .
  .   .   .
  .   .   .
  .   .   .
  .   .   .
  </code></pre>
  <p>Any idea on how to do that ?</p>
  <p>Thanks i advance.</p>