title: Filtering out values of a bidimensional array
body: <p>I have a bidimensional array which looks like this:</p>
  
  <pre><code>[[10, 20, 30, S1]
  [10, 20, 30, S1]
  [10, 20, 30, S1]
  [50, 70, 80, G1]
  [50, 70, 80, G1]
  [50, 70, 80, G1]]
  </code></pre>
  
  <p>I want to filter out every "non-first" occurence of the 4th value of each sub-array, like this:</p>
  
  <pre><code>[[10, 20, 30, S1]
  [10, 20, 30]
  [10, 20, 30]
  [50, 70, 80, G1]
  [50, 70, 80]
  [50, 70, 80]]
  </code></pre>
  
  <p>How is this possible?
  Thanks in advance</p>