title: ruby - array of arrays - how to select unique elements?
body: <p>I have a "Q&amp;A" array and each element is a subarray of three elements (Q, A and Animal).
  How can I select all the unique animals?</p>
  
  <p>I can select the animals alone with:</p>
  
  <pre><code>[@q_and_a[0][2]] + [@q_and_a[1][2]] + [@q_and_a[2][2]] +[@q_and_a[3][2]] 
  # =&gt; ["Elephant", "Elephant", "Spider", "Spider"]
  </code></pre>