title: pyspark: convert a bytearray field to string in data frame
body: <p>I am reading a parquet file to a dataframe:</p>
  
  <pre><code>my_df = sqlContext.read.parquet('hdfs://my_server/user/hive/warehouse/my_db.db/my_table')
  </code></pre>
  
  <p>if I do:</p>
  
  <pre><code>my_df.head()
  </code></pre>
  
  <p>I got:</p>
  
  <pre><code>Row(id=bytearray(b'00000000000000000000000000000000'), numcores=8, ...)
  </code></pre>
  
  <p>and when I do </p>
  
  <pre><code>my_df.show()
  </code></pre>
  
  <p>the first field id looks like:</p>
  
  <pre><code>[30 30 30 30 30 3...]
  </code></pre>
  
  <p>How do I change the bytearray field and make it show as a string output? Thanks!</p>