Using Scala groupBy(), from method fetchUniqueCodesForARootCode(). I want to get a map from rootCodes to lists of uniqueCodes - scala

Question

I want to to return Future[Map[String, List[String]]] from fetchUniqueCodesForARootCode method
import scala.concurrent._
import ExecutionContext.Implicits.global
case class DiagnosisCode(rootCode: String, uniqueCode: String, description: Option[String] = None)
object Database {
private val data: List[DiagnosisCode] = List(
DiagnosisCode("A00", "A001", Some("Cholera due to Vibrio cholerae")),
DiagnosisCode("A00", "A009", Some("Cholera, unspecified")),
DiagnosisCode("A08", "A080", Some("Rotaviral enteritis")),
DiagnosisCode("A08", "A083", Some("Other viral enteritis"))
)
def getAllUniqueCodes: Future[List[String]] = Future {
Database.data.map(_.uniqueCode)
}
def fetchDiagnosisForUniqueCode(uniqueCode: String): Future[Option[DiagnosisCode]] = Future {
Database.data.find(_.uniqueCode.equalsIgnoreCase(uniqueCode))
}
}
getAllUniqueCodes returns all unique codes from data List.
fetchDiagnosisForUniqueCode returns DiagnosisCode when uniqueCode matches.
From fetchDiagnosisForUniqueCodes, I am returningFuture[List[DiagnosisCode]] using getAllUniqueCodes() and fetchDiagnosisForUniqueCode(uniqueCode).*
def fetchDiagnosisForUniqueCodes: Future[List[DiagnosisCode]] = {
val xa: Future[List[Future[DiagnosisCode]]] = Database.getAllUniqueCodes.map { (xs:
List[String]) =>
xs.map { (uq: String) =>
Database.fetchDiagnosisForUniqueCode(uq)
}
}.map(n =>
n.map(y=>
y.map(_.get)))
}
xa.flatMap {
listOfFuture =>
Future.sequence(listOfFuture)
}}
Now, def fetchUniqueCodesForARootCode should return Future[Map[String, List[DiagnosisCode]]] using fetchDiagnosisForUniqueCodes and groupBy
Here is the method
def fetchUniqueCodesForARootCode: Future[Map[String, List[String]]] = {
fetchDiagnosisForUniqueCodes.map { x =>
x.groupBy(x => (x.rootCode, x.uniqueCode))
}
}
Need to get the below result from fetchUniqueCodesForARootCode:-
A00 -> List(A001, A009), H26 -> List(H26001, H26002), B15 -> List(B150, B159), H26 -> List(H26001, H26002)

Answer 1

It's hard to decode from the question description, what the problem is. But if I understood correctly, you want to get a map from rootCodes to lists of uniqueCodes.
The groupBy method takes a function that for every element returns its key. So first you have to group by the rootCodes and then you have to use map to get the correct values.
groupBy definition: https://dotty.epfl.ch/api/scala/collection/IterableOps.html#groupBy-f68
scastie: https://scastie.scala-lang.org/KacperFKorban/PL1X3joNT3qNOTm6OQ3VUQ