title: Find the maximum and minimum value of every column and then find the maximum and minimum value of every row
body: <p>I've got this matrix:</p>
  
  <pre><code>a &lt;- matrix(rnorm(1000 * 18, mean = 100, sd = sqrt(10)), 1000, 18)
  </code></pre>
  
  <p>I would like to find the maximum and minimum value of every column and the maximum and minimum value of every row.</p>