title: What's the proper way to map over a single column in a DataFrame?
body: <p>Usually I do something like</p>
  
  <pre class="lang-scala prettyprint-override"><code>val fun = udf { x =&gt; ... }
  df.withColumn("new", fun(df.col("old"))).drop("old").withColumnRename("new", "old")
  </code></pre>
  
  <p>is there a shorter way?</p>