title: What does "!" mean in scala?
body: <p>I am looking at a piece of code with the following:</p>
  
  <p><code>graph.vertices.filter(!_._2._1)</code></p>
  
  <p>I understand that <code>_</code> are wildcard characters in <code>scala</code> but I do not know what the <code>!</code> is supposed to do. </p>
  
  <p>What does <code>!</code> mean in scala?</p>