title: Removing elements from array Ruby
body: <p>Let's say I am trying to remove elements from array <code>a = [1,1,1,2,2,3]</code>. If I perform the following:</p>
  
  <pre><code>b = a - [1,3]
  </code></pre>
  
  <p>Then I will get:</p>
  
  <pre><code>b = [2,2]
  </code></pre>
  
  <p>However, I want the result to be</p>
  
  <pre><code>b = [1,1,2,2]
  </code></pre>
  
  <p>i.e. I only remove one instance of each element in the subtracted vector not all cases. Is there a simple way in Ruby to do this?</p>