title: How to get item from vector struct in PySpark
body: <p>I am trying to get scores array from TF-IDF result vector.
  For example:</p>
  
  <pre><code>rescaledData.select("words", "features").show()
  +-----------------------------+---------------------------------------------------------------------------------------------+
  |words                        |features                                                                                     |
  +-----------------------------+---------------------------------------------------------------------------------------------+
  |[a, b, c]                    |(4527,[0,1,31],[0.6363067860791387,1.0888040725098247,4.371858972705023])                    |
  |[d]                          |(4527,[8],[2.729945780576634])                                                               |
  +-----------------------------+---------------------------------------------------------------------------------------------+
  </code></pre>
  
  <pre><code>rescaledData.select(rescaledData['features'].getItem('values')).show()
  </code></pre>
  
  <p>But instead of array i got an error.</p>
  
  <pre><code>AnalysisException: u"Can't extract value from features#1786: need struct type but got struct&lt;type:tinyint,size:int,indices:array&lt;int&gt;,values:array&lt;double&gt;&gt;;"
  </code></pre>
  
  <p>What i want is</p>
  
  <pre><code>+--------------------------+-----------------------------------------------------------+
  |words                     |features                                                   |
  +--------------------------+-----------------------------------------------------------+
  |[a, b, c]                 |[0.6363067860791387, 1.0888040725098247, 4.371858972705023]|
  +--------------------------+-----------------------------------------------------------+
  </code></pre>
  
  <p>How to fix this?</p>