Scala example source code file (FreqMap.scala)

This example Scala source code file (FreqMap.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

float, float, freqmap, freqmap, int, list, none, none, some, t, t

The Scala FreqMap.scala source code

/*-------------------------------------------------------------------------*\
**  ScalaCheck                                                             **
**  Copyright (c) 2007-2010 Rickard Nilsson. All rights reserved.          **
**  http://www.scalacheck.org                                              **
**                                                                         **
**  This software is released under the terms of the Revised BSD License.  **
**  There is NO WARRANTY. See the file LICENSE for the full text.          **
\*-------------------------------------------------------------------------*/

package org.scalacheck.util

trait FreqMap[T] {
  protected val underlying: scala.collection.immutable.Map[T,Int]
  val total: Int
 
  def +(t: T) = new FreqMap[T] {
    private val n = FreqMap.this.underlying.get(t) match {
      case None => 1
      case Some(n) => n+1
    }
    val underlying = FreqMap.this.underlying + (t -> n)
    val total = FreqMap.this.total + 1
  }

  def -(t: T) = new FreqMap[T] {
    val underlying = FreqMap.this.underlying.get(t) match {
      case None => FreqMap.this.underlying
      case Some(n) => FreqMap.this.underlying + (t -> (n-1))
    }
    val total = FreqMap.this.total + 1
  }

  def ++(fm: FreqMap[T]) = new FreqMap[T] {
    private val keys = FreqMap.this.underlying.keySet ++ fm.underlying.keySet 
    private val mappings = keys.toStream.map { x => 
      (x, fm.getCount(x).getOrElse(0) + FreqMap.this.getCount(x).getOrElse(0))
    }
    val underlying = scala.collection.immutable.Map(mappings: _*)
    val total = FreqMap.this.total + fm.total
  }
 
  def --(fm: FreqMap[T]) = new FreqMap[T] {
    val underlying = FreqMap.this.underlying transform {
      case (x,n) => n - fm.getCount(x).getOrElse(0)
    }
    lazy val total = (0 /: underlying.valuesIterator) (_ + _)
  }
 
  def getCount(t: T) = underlying.get(t)
 
  def getCounts: List[(T,Int)] = underlying.toList.sortBy(-_._2)
 
  def getRatio(t: T) = for(c <- getCount(t)) yield (c: Float)/total
 
  def getRatios = for((t,c) <- getCounts) yield (t, (c: Float)/total)

  override def toString = underlying.toString
}
 
object FreqMap {
  def empty[T] = new FreqMap[T] {
    val underlying = scala.collection.immutable.Map.empty[T,Int]
    val total = 0
  }
}