title: select individual 2 user groups in single table?
body: <p>I have a table like this and I want to select 12 groups among 25 users, but users cannot appear more than once in either column. It is for for my research work. </p>
  
  <pre><code>userx   usery   final
  user1   user9   0
  user2   user21  0
  user3   user20  1.86603810646243E-02
  user4   user14  0
  user5   user13  0
  user6   user12  0
  user7   user11  0
  user8   user10  0
  user9   user23  5.2301255230118E-03
  user10  user12  5.13300861745978E-02
  user11  user15  1.6096147655314E-03
  user12  user19  2.1337126600292E-03
  user12  user22  2.1337126600292E-03
  user13  user18  3.3259423503309E-03
  user14  user21  7.657805491741E-04
  user15  user16  5.4939136055145E-03
  user16  user21  5.3359468583246E-03
  user17  user18  1.49153302680261E-02
  user18  user21  0.004619445666522
  user19  user22  0
  user20  user24  2.6088701585401E-03
  user21  user23  2.01673460630756E-02
  user22  user23  0.05878423513694
  user23  user24  2.21079691516702E-02
  user24  user25  4.57905347028916E-02
  </code></pre>