title: Get numbers characters from a string
body: <p>How to get numbers characters from a string? I don't want to convert  in <code>Int</code>.</p>
  
  <pre><code>var string = "string_1"
  var string2 = "string_20_certified"
  </code></pre>
  
  <p>My result have to be formatted like this:</p>
  
  <pre><code>newString = "1"
  newString2 = "20"
  </code></pre>