Scala Reduce操作（简化归约）reduce和fold

 1 package chapter07
 2
 3 object Test15_HighLevelFunction_Reduce {
 4   def main(args: Array[String]): Unit = {
 5     val list = List(1,2,3,4)
 6
 7     // 1. reduce
 8     println(list.reduce( _ + _ ))
 9     println(list.reduceLeft(_ + _))
10     println(list.reduceRight(_ + _))
11
12     println("===========================")
13
14     val list2 = List(3,4,5,8,10)
15     println(list2.reduce(_ - _))    // -24
16     println(list2.reduceLeft(_ - _))  //-24
17     println(list2.reduceRight(_ - _))    // 3 - (4 - (5 - (8 - 10))), 6
18
19     println("===========================")
20     // 2. fold
21     println(list.fold(10)(_ + _))     // 10 + 1 + 2 + 3 + 4
22     println(list.foldLeft(10)(_ - _))    // 10 - 1 - 2 - 3 - 4
23     println(list2.foldRight(11)(_ - _))    // 3 - (4 - (5 - (8 - (10 - 11)))),  -5
24   }
25 }