title: How to shuffle the rows in a Spark dataframe?
body: <p>I have a dataframe like this:</p>
  
  <pre><code>+---+---+
  |_c0|_c1|
  +---+---+
  |1.0|4.0|
  |1.0|4.0|
  |2.1|3.0|
  |2.1|3.0|
  |2.1|3.0|
  |2.1|3.0|
  |3.0|6.0|
  |4.0|5.0|
  |4.0|5.0|
  |4.0|5.0|
  +---+---+
  </code></pre>
  
  <p>and I would like to shuffle all the rows using Spark in Scala.</p>
  
  <p>How can I do this without going back to RDD?</p>