title: Finding elements that do not overlap between two vectors
body: <p>I'm trying to identify elements which are not included in the other vector. For instance in two vectors I have</p>
  
  <pre><code>list.a &lt;- c("James", "Mary", "Jack", "Sonia", "Michelle", "Vincent")
  
  list.b &lt;- c("James", "Sonia", "Vincent")
  </code></pre>
  
  <p>is there a way to verify which people do not overlap? In the example, I would want to get the vector result that contains Mary, Jack, and Michelle.</p>
  
  <p>Any suggestions will help!</p>