title: Selecting or removing duplicate columns from spark dataframe
body: <p>Given a spark dataframe, with a duplicate columns names (eg. <code>A</code>) for <strong>which I cannot modify the upstream or source</strong>, how do I select, remove or rename one of the columns so that I may retrieve the columns values?</p>
  
  <p><code>df.select('A')</code> shows me an ambiguous column error, as does <code>filter</code>, <code>drop</code>, and <code>withColumnRenamed</code>. How do I select one of the columns?</p>