title: Finding rows with a unique combination of values (R)
body: <p>This is a bit more complicated that the title lets on, and I'm sure if I could think of a way to better describe it, I could google it better.  </p>
  
  <p>I have data that looks like this:</p>
  
  <pre><code>SET                     ID    
  100301006              1287025
  100301006              1287026
  100301010              1287027
  100301013              1287030
  100301011              1287027
  </code></pre>
  
  <p>and I would like to identify and select those rows where each both values in a row have a unique value for the column.  In the example above, I want to grab only the row:</p>
  
  <pre><code>100301013              1287030
  </code></pre>
  
  <p>I don't want <code>SET</code> <code>100301006</code>, since it matches to 2 different records in the ID field (<code>1287025</code> and <code>1287026</code>).  Similarly, I don't want SET <code>100301010</code> since the <code>ID</code> record it matches to (<code>1287027</code>) can also match another SET (<code>10030011</code>).</p>
  
  <p>In some cases there could be more than 2 matches.</p>
  
  <p>I could do this in loops, but that seems like a hack.  I'd love a base R or data.table solution, but I'm not so interested in dplyr (trying to minimize dependencies).</p>