title: How do I compare elements of one row with every other row in the same matrix
body: <p>I have the matrix:</p>
  
  <pre><code>a = [ 1 2 3 4;
        2 4 5 6;
        4 6 8 9]
  </code></pre>
  
  <p>and I want to compare every row with every other two rows one by one. If they share the same key then the result will tell they have a common key.</p>