title: How do I display a long number in groups?
body: <p>I have a string</p>
  
  <pre><code>string = '1234432198766789'
  </code></pre>
  
  <p>I want it to look like this:</p>
  
  <pre><code>"1234 4321 9876 6789"
  </code></pre>
  
  <p>What is the best way to do it? I am able to use Rails' String extensions.</p>
  
  <p>I don't want to modify the original string, so <code>insert</code> method couldn't be used.</p>