Scalaで重み付き乱択アルゴリズム ref: http://qiita.com/items/9fab26545ae931a1dc67

chooser.scala

    val makeRandomChooser = (shops : List[Shop]) => {
        val sortedList = shops.sort(_.likely > _.likely)
        var likeSum = 0.0
        sortedList.foreach(likeSum += _.likely)
        val targetList = sortedList.map{tem => new Shop(0, tem.name, tem.likely / likeSum)}
        println(targetList)

        sortedList.foreach(likeSum += _.likely)

        def choosen (targetList : List[Shop], likeSum : Double) = {
            val rand = Math.random
            var sum = 0.0
            val result = targetList.find{(shop: Shop) =>
                sum += shop.likely
                rand < sum
            }
            if(result == None){
                targetList.last
            } else {
                result.get
            }
        }
        choosen(targetList, likeSum)
    }