title: How to filter a list in J?
body: <p>I'm currently learning the fascinating J programming language, but one thing I have not been able to figure out is how to filter a list.</p>
  
  <p>Suppose I have the arbitrary list <code>3 2 2 7 7 2 9</code> and I want to remove the 2s but leave everything else unchanged, i.e., my result would be <code>3 7 7 9</code>. How on earth do I do this?</p>