title: Initializing 2 dimensional array
body: <p>I need to initialize 2 dimensional array with m rows and n columns, but <code>m</code> and <code>n</code> might change. I found here example like this :</p>
  
  <pre><code>ARRAY[[NULL,NULL],[NULL,NULL]] 
  </code></pre>
  
  <p>But it initializes array with 2 rows and 2 columns.</p>