title: how to output the adjacency group from edge list?
body: <p>Edge list:</p>
  
  <pre><code>el &lt;- rbind(c(6,11), c(1,8), c(8,12), c(11,17), 
              c(6,7), c(7,11), c(18,19), c(6,16))
  </code></pre>
  
  <p>In this case, 6,11,17,7,16 connect, 1,8,2 connect, and 18,19 connect with each other. So there are three groups. How to get these groups from this edge list using R?</p>