dynamic_sorting.scala

// Runs in a SBT console with scalaz references in Build.sbt

import scalaz._, Scalaz._

case class Person(age: Int, name: String)

object PeopleSort {
  def sort(people: List[Person], fields: List[String]): List[Person] = {
    val ordering = getScalaOrdering(fields)
    people.sorted(ordering)
  }

  def getScalaOrdering(fields: List[String]) = {
    // Converts the List[String] to a List[scalaz.Order]
    val orders = fields.map(s => sorts(s))

    // Reduces all the `Order`s into a single `Order` and converts to a `scala.Ordering`
    Foldable[List].fold(orders).toScalaOrdering
  }

  val sorts = Map(
    "age"  -> Order.orderBy[Person, Int](_.age), 
    "name" -> Order.orderBy[Person, String](_.name)
  )  
}

/* Example */

val people = List(
  Person(50, "Zack"),
  Person(50, "Jane"),
  Person(50, "Bob"),
  Person(40, "Yasmine")
)

PeopleSort.sort(people, List("age"))          // List(Person(40,Yasmine), Person(50,Zack), Person(50,Jane), Person(50,Bob))
PeopleSort.sort(people, List("name"))         // List(Person(50,Bob), Person(50,Jane), Person(40,Yasmine), Person(50,Zack))
PeopleSort.sort(people, List("age", "name"))  // List(Person(40,Yasmine), Person(50,Bob), Person(50,Jane), Person(50,Zack))