title: How to strip special characters out of string?
body: <p>I have a set with the characters I allow in my string:</p>
  
  <pre><code>var characterSet:NSCharacterSet = NSCharacterSet(charactersInString: "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLKMNOPQRSTUVWXYZ")
  </code></pre>
  
  <p>I want to strip <em>any other</em> characters from a string so two unformatted data can be considered equal, like this:</p>
  
  <pre><code>"American Samoa".lowercaseString == "american_samoa1".lowercaseString
  </code></pre>
  
  <p>the lowercase version of these transformed strings would be <code>"americansamoa"</code></p>