title: Detect which elements were added to an array in ruby
body: <p>I have 2 arrays :</p>
  
  <pre><code>arr1 = [1,2,3,4]
  arr2 = [1,2, 82, 167,3,79,4]
  </code></pre>
  
  <p>I want to implement a function that realize the following</p>
  
  <pre><code>new_elems(arr1, arr2)
  #=&gt; [82,167,79]
  </code></pre>
  
  <p>Is there a ruby function for this? </p>
  
  <p>Thank you</p>
  
  <p><strong>EDIT:</strong></p>
  
  <p>Array#- would answer to this question. What about the performances then ? Let's say I have a thousands elements array. Would Array#- have acceptable performances ?</p>