title: How do I flatten an array in Ruby?
body: <p>On Ruby. I have array of array <code>c = [["a"], ["b"]]</code></p>
  
  <p>How convert it to <code>c = a + b</code></p>
  
  <pre><code>c = ["a", "b"]
  </code></pre>
  
  <p>for any array. Maybe it is possible not using other variables.
  All array inside not flatten.</p>
  
  <pre><code>d = [ [["a"], ["b"]], [["c"], ["d"]], [["e"], ["f"]] ] 
  </code></pre>
  
  <p>I need <code>[ [["a"], ["b"], ["c"], ["d"], ["e"], ["f"]] ]</code></p>