title: How to get date and time from string?
body: <p>I have a data frame with the following schema:</p>
  
  <pre><code>  root
  
    |-- date : string (nullable = true)
  </code></pre>
  
  <p>The value looks like <code>201605250000</code>. How can I extract date, hour and mm from this string?</p>