title: In pyspark, how do you add/concat a string to a column?
body: <p>I would like to add a string to an existing column. For example, <code>df['col1']</code> has values as <code>'1', '2', '3'</code> etc and I would like to concat string <code>'000'</code> on the left of <code>col1</code> so I can get a column (new or replace the old one doesn't matter) as <code>'0001', '0002', '0003'</code>. </p>
  
  <p>I thought I should use <code>df.withColumn('col1', '000'+df['col1'])</code> but of course it does not work since pyspark dataframe are immutable?</p>
  
  <p>This should be an easy task but i didn't find anything online. Hope someone can give me some help!</p>
  
  <p>Thank you!</p>