title: Column alias after groupBy in pyspark
body: <p>I need the resulting data frame in the line below, to have an alias name "maxDiff" for the max('diff') column after groupBy. However, the below line does not makeany change, nor throw an error.   </p>
  
  <pre><code> grpdf = joined_df.groupBy(temp1.datestamp).max('diff').alias("maxDiff")
  </code></pre>