title: Converting string time to day timestamp
body: <p>I have just started working for Pyspark, and need some help converting a column datatype. 
  My dataframe has a string column, which stores the time of day in AM/PM, and I need to convert this into datetime for further processing/analysis.</p>
  
  <pre><code>fd = spark.createDataFrame([(['0143A'])], ['dt'])
  fd.show()
  
  +-----+
  |   dt|
  +-----+
  |0143A|
  +-----+
  
  from pyspark.sql.functions import date_format, to_timestamp
  #fd.select(date_format('dt','hhmma')).show()
  fd.select(to_timestamp('dt','hhmmaa')).show()
  
  +----------------------------+
  |to_timestamp(`dt`, 'hhmmaa')|
  +----------------------------+
  |                        null|
  +----------------------------+
  
  Expected output: 01:43
  
  </code></pre>
  
  <p>How can I get the proper datetime format in the above scenario?</p>
  
  <p>Thanks for your help!</p>