title: Randomly change/mutate one value in a list
body: <p>I'm writing a genetic algorithm and want to randomly mutate a number within a list.</p>
  
  <p>If I had a list, for example:</p>
  
  <pre><code>[1,2,3,4,5]
  </code></pre>
  
  <p>How could I take the list and change just one of the numbers to a random number, for example:</p>
  
  <pre><code>[1,2,7,4,5]
  </code></pre>
  
  <p>or </p>
  
  <pre><code>[1,3,3,4,5]
  </code></pre>