title: convert scientific notation in string format to numeric in spark dataframe
body: <pre><code>Day_Date,timeofday_desc,Timeofday_hour,Timeofday_minute,Timeofday_second,value
  2017-12-18,12:21:02 AM,0,21,2,“1.779209040E+08”
  2017-12-19,12:21:02 AM,0,21,2,“1.779209040E+08”
  2017-12-20,12:30:52 AM,0,30,52,“1.779209040E+08”
  2017-12-21,12:30:52 AM,0,30,52,“1.779209040E+08”
  2017-12-22,12:47:10 AM,0,47,10,“1.779209040E+08”
  2017-12-23,12:47:10 AM,0,47,10,“1.779209040E+08”
  2017-12-24,02:46:59 AM,2,46,59,“1.779209040E+08”
  2017-12-25,02:46:59 AM,2,46,59,“1.779209040E+08”
  2017-12-26,03:10:27 AM,3,10,27,“1.779209040E+08”
  2017-12-27,03:10:27 AM,3,10,27,“1.779209040E+08”
  2017-12-28,03:52:08 AM,3,52,8,“1.779209040E+08”
  </code></pre>
  
  <p>I am trying to convert <code>value</code> column to <code>177920904</code> </p>
  
  <pre><code>val df1 = df.withColumn("s", 'value.cast("Decimal(10,4)")).drop("value").withColumnRenamed("s", "value")
  </code></pre>
  
  <p>also tried casting value as <code>Float</code>, <code>Double</code>. Always get null as output</p>
  
  <pre><code>df1.select("value").show()
  
  
  +-----------+
  |   value   |
  +-----------+
  |       null|
  |       null|
  |       null|
  |       null|
  |       null|
  |       null|
  |       null|
  |       null|
  </code></pre>
  
  <hr>
  
  <pre><code>df.printSchema
  
  root
   |-- Day_Date: string (nullable = true)
   |-- timeofday_desc: string (nullable = true)
   |-- Timeofday_hour: string (nullable = true)
   |-- Timeofday_minute: string (nullable = true)
   |-- Timeofday_second: string (nullable = true)
   |-- value: string (nullable = true)
  </code></pre>