title: Remove values from IDL array
body: <p>I have a variable named <code>wl</code> which has a value range from 900 to 30000, another variable name <code>f</code> is dependent on it. I want to remove values below 1280 from both of these variables.  </p>
  
  <p>What I've done is</p>
  
  <pre><code>pO = WHERE(wl &lt; 1280)
  </code></pre>
  
  <p>But when I remove them with <code>remove</code> it can't remove error since it needs an array of indices to remove and checking the type of <code>pO</code> yields <code>long</code>.</p>