title: How to convert multiple columns i.e time ,year,month and date into datetime format in pyspark dataframe
body: <p>Data frame has 4 columns year,month,date,hhmm </p>
  
  <p>hhmm - is hour and minute concatenated 
  eg: 10:30 is equal to 1030</p>
  
  <pre><code>dd=spark.createDataFrame([(2019,2,13,1030),(2018,2,14,1000),(2029,12,13,0300)],["Year","month","date","hhmm"])
  dd.collect()
  </code></pre>
  
  <p>expected output in datetime format in pyspark dataframe dd</p>
  
  <pre><code>dd.collect()
  2019-02-13 10:30:00 
  2018-2-14 10:00:00  
  2019-12-13 03:00:00 
  </code></pre>