title: How to filter a spark's dataframe array with scala
body: <p>I'm a beginner with Scala.</p>
  
  <p>I've got a dataframe with 2 columns :</p>
  
  <p>the first is a date, the second an array of words.</p>
  
  <pre><code>created_at:string
  words:array
      element:string
  </code></pre>
  
  <p>I wish to keep only words begining with a '#'</p>
  
  <p>I would prefer to make the filter before exploding the array, as most words do not start with a '#'</p>
  
  <p>I didn't find a way to modify an array column and apply something like a filter(_.startsWith("#")).</p>
  
  <p>Is it possible ? and how ?</p>
  
  <p>Thank's</p>
  
  <p>Pierre</p>