title: Convert comma separated string to array in pyspark dataframe
body: <p>I have a dataframe as below where ev is of type string.</p>
  
  <pre><code>&gt;&gt;&gt; df2.show()
  +---+--------------+
  | id|            ev|
  +---+--------------+
  |  1| 200, 201, 202|
  |  1|23, 24, 34, 45|
  |  1|          null|
  |  2|            32|
  |  2|          null|
  +---+--------------+
  </code></pre>
  
  <p>Is there a way to cast ev to type ArrayType without using UDF or UDF is the only option to do that?</p>