How to find Minimum in a sequence - scala

Question

A = ... //tuples of Medication(patientid,date,medicine)
B = A.groupby(x => x.patientid)
Example B would look like below - now I need to find the minimum date, how to do that in scala??
(
478009505-01,
CompactBuffer(
Some(Medication(478009505-01,Fri Jun 12 10:30:00 EDT 2009,glimepiride)),
Some(Medication(478009505-01,Fri Jun 12 10:30:00 EDT 2009,glimepiride)),
Some(Medication(478009505-01,Fri Jun 12 10:30:00 EDT 2009,glimepiride))
)
)

Answer 1

Making some assumptions on the types:
case class Medication(id: Int, date: String, medicine: String)
val l = List(
Some(Medication(478009505, "Fri Jun 12 10:30:00 EDT 2010", "glimepiride")),
Some(Medication(478009505, "Fri Jun 12 10:30:00 EDT 2008", "glimepiride")),
None,
Some(Medication(478009505, "Fri Jun 12 10:30:00 EDT 2011", "glimepiride"))
)
You can use a for comprehension to extract all the dates, then get the min with minBy:
import java.text.SimpleDateFormat
val format = new SimpleDateFormat("EEE MMM dd hh:mm:ss zzz yyyy")
def createDateTime(s: String) = new Date(format.parse(s).getTime))
val dates = for {
optMed <- l // foreach item
med <- optMed // if it contains some value
} yield createDateTime(med.date) // create a comparable date
dates.minBy(_.getTime) // get the minimum date
The result is the oldest date(2008-06-12)