title: Does dataFrameWriter partitionBy shuffle the data?
body: <p>I have data partitioned in one way, I just want to partition it in another.
  So it basically gonna be something like this:</p>
  
  <pre class="lang-java prettyprint-override"><code>sqlContext.read().parquet("...").write().partitionBy("...").parquet("...")
  </code></pre>
  
  <p>I wonder does this will trigger shuffle or all data will be re-partition locally, because in this context a partition means just a directory in HDFS and data from the same partition doesn't have to be on the same node to be written in the same dir in HDFS.</p>