title: How to get an array "complement" of another?
body: <p>the easiest way for me to explain what i want is with an example:</p>
  
  <pre><code>a = 1:20
  
  b = [2,7,12,18]
  </code></pre>
  
  <p>Now I want <code>c</code> to be <code>[1,3,4,5,6,8,...,19,20]</code> with length <code>16</code>: <code>length(a) - length(b)</code> of course.</p>
  
  <p>Is there a way for me to get <code>c</code>?</p>