title: Remove duplicate element pairs from multidimensional array
body: <p>I have an array that looks like this:</p>
  
  <pre><code>1.  coordinates = [ [16.343345, 35.123523],
  2.                  [14.325423, 34.632723],
  3.                  [15.231512, 35.426914],
  4.                  [16.343345, 35.123523],
  5.                  [15.231512, 32.426914] ]
  </code></pre>
  
  <p>The latitude on line 5 is the same as on line 3, but they have different longitudes and are therefore not duplicates.</p>
  
  <p>Both the latitude and longitude are the same on line 3 and 6, and are therefore duplicates and one should be removed.</p>