Try instead:
import org.apache.spark.sql.functions._
val determineDayPartID = udf((evntStDate: String, evntStHour: String) => {
val stFormat = new java.text.SimpleDateFormat("yyMMdd")
var stDateStr:String = evntStDate.substring(2,8)
val stDate:Date = stFormat.parse(stDateStr)
val stHour = evntStHour.substring(1,3).toDouble + 0.1
var bucket = Math.ceil(stHour/3.0).toInt
val cal:Calendar = Calendar.getInstance
cal.setTime(stDate)
var dayOfWeek = cal.get(Calendar.DAY_OF_WEEK)
if (dayOfWeek == 1) dayOfWeek = 8
if (dayOfWeek > 6) bucket = bucket + 8
bucket
})
input.withColumn("DayPartID", determineDayPartID (col("StartDate"),
col("EventStartHour")))
