title: Pig Filter out NOT Matches
body: <p>I have a bunch of strings that have various prefixes including "unknown:"  I'd really like to filter out all the strings starting with "unknown:" in my Pig script, but it doesn't appear to work.</p>
  
  <p><code>simpleFilter = FILTER records BY NOT(mystr MATCHES '^unknown');</code></p>
  
  <p>I've tried a few other permutations of the regex, but it appears that <code>MATCHES</code> just doesn't work well with NOT.  Am I missing something?</p>
  
  <p>Using Pig 0.9.2</p>