title: How to select an aggregated column from a dataframe
body: <p><code>df = df.groupby(F.upper(F.col('count'))).agg({'totalvis.age':'avg'}).show()</code> creates <code>avg(totalvis.age AS </code>age<code>)</code> column.</p>
  <p>I want to use another aggregate function to select max of the newly created column, but there is an issue with column name not being resolvable.</p>