title: Count number of non null matrix elements
body: <p>I have an array of arrays something like <code>arr[26,20]</code> with the alphabet in the first position of each array.</p>
  
  <p>So laid out in matrix form it would something like.</p>
  
  <ul>
  <li>ABCDEFGHIJKLMNOPQRSTUVWXYZ</li>
  <li>//////////////////////////</li>
  <li>//////////////////////////</li>
  <li>//////////////////////////</li>
  <li>//////////////////////////</li>
  </ul>
  
  <p>The forward slashes representing null values.</p>
  
  <p>I'm trying to get the number of non null elements in a single colomn.</p>
  
  <p>So the code I could use on a normal array would be</p>
  
  <pre><code>int number = arr[0].Count(s =&gt; s != null);
  </code></pre>
  
  <p>However, how would I do this for a matrix like described?</p>