title: How to subtract 2 string columns in a Pyspark dataframe
body: <p>Below is the scenario:
  Consider a Pyspark dataframe having 2 columns like below:</p>
  <p>{
  fullname: facebook,
  lastname: book
  }</p>
  <p>I want a new column firstname by subracting fullname and lastname like below</p>
  <p>{
  firstname:face,
  lastname:book
  }</p>