Ranking methods: Difference between revisions

=={{header|Scala}}==

This example uses a type-safe singly-linked object model with no mutable state variables, which makes it longer than the Ruby version but demonstrates object-oriented functional programming style.

<lang Scala>object RankingMethods extends App {

case class Score(score: Int, name: String) // incoming data

case class Rank[Precision](rank: Precision, names: List[String]) // outgoing results (can be int or double)

case class State[Precision](n: Int, done: List[Rank[Precision]]) { // internal state, no mutable variables

def next(n: Int, next: Rank[Precision]) = State(n, next :: done)

}

def grouped[Precision](list: List[Score]) = // group names together by score, with highest first

(scala.collection.immutable.TreeMap[Int, List[Score]]() ++ list.groupBy(-_.score))

.values.map(_.map(_.name)).foldLeft(State[Precision](1, Nil)) _

// Ranking methods:

def rankStandard(list: List[Score]) =

grouped[Int](list){case (state, names) => state.next(state.n+names.length, Rank(state.n, names))}.done.reverse

def rankModified(list: List[Score]) =

rankStandard(list).map(r => Rank(r.rank+r.names.length-1, r.names))

def rankDense(list: List[Score]) =

grouped[Int](list){case (state, names) => state.next(state.n+1, Rank(state.n, names))}.done.reverse

def rankOrdinal(list: List[Score]) =

list.zipWithIndex.map{case (score, n) => Rank(n+1, List(score.name))}

def rankFractional(list: List[Score]) =

rankStandard(list).map(r => Rank((2*r.rank+r.names.length-1.0)/2, r.names))

// Tests:

def parseScores(s: String) = s split "\\s+" match {case Array(s,n) => Score(s.toInt, n)}

val test = List("44 Solomon", "42 Jason", "42 Errol", "41 Garry", "41 Bernard", "41 Barry", "39 Stephen").map(parseScores)

println("Standard:")

println(rankStandard(test) mkString "\n")

println("\nModified:")

println(rankModified(test) mkString "\n")

println("\nDense:")

println(rankDense(test) mkString "\n")

println("\nOrdinal:")

println(rankOrdinal(test) mkString "\n")

println("\nFractional:")

println(rankFractional(test) mkString "\n")

}</lang>

{{out}}

<pre>Standard:

Rank(1,List(Solomon))

Rank(2,List(Jason, Errol))

Rank(4,List(Garry, Bernard, Barry))

Rank(7,List(Stephen))

Modified:

Rank(1,List(Solomon))

Rank(3,List(Jason, Errol))

Rank(6,List(Garry, Bernard, Barry))

Rank(7,List(Stephen))

Dense:

Rank(1,List(Solomon))

Rank(2,List(Jason, Errol))

Rank(3,List(Garry, Bernard, Barry))

Rank(4,List(Stephen))

Ordinal:

Rank(1,List(Solomon))

Rank(2,List(Jason))

Rank(3,List(Errol))

Rank(4,List(Garry))

Rank(5,List(Bernard))

Rank(6,List(Barry))

Rank(7,List(Stephen))

Fractional:

Rank(1.0,List(Solomon))

Rank(2.5,List(Jason, Errol))

Rank(5.0,List(Garry, Bernard, Barry))

Rank(7.0,List(Stephen))</pre>