Scala Map操作

package chapter07

object Test14_HighLevelFunction_Map {
  def main(args: Array[String]): Unit = {
    val list = List(1,2,3,4,5,6,7,8,9)

    // 1. 过滤
    // 选取偶数
    val evenList = list.filter( (elem: Int) => {elem % 2 == 0} )
    println(evenList)

    // 选取奇数
    println(list.filter( _ % 2 == 1 ))

    println("=======================")

    // 2. 映射map
    // 把集合中每个数乘2
    println(list.map(_ * 2))
    println(list.map( x => x * x))

    println("=======================")

    // 3. 扁平化
    val nestedList: List[List[Int]] = List(List(1,2,3),List(4,5),List(6,7,8,9))

    val flatList = nestedList(0) ::: nestedList(1) ::: nestedList(2)
    println(flatList)

    val flatList2 = nestedList.flatten
    println(flatList2)

    println("=======================")

    // 4. 扁平映射
    // 将一组字符串进行分词，并保存成单词的列表
    val strings: List[String] = List("hello world", "hello scala", "hello java", "we study")
    val splitList: List[Array[String]] = strings.map( _.split(" ") )    // 分词
    val flattenList = splitList.flatten    // 打散扁平化

    println(flattenList)

    val flatmapList = strings.flatMap(_.split(" "))
    println(flatmapList)

    println("========================")

    // 5. 分组groupBy
    // 分成奇偶两组
    val groupMap: Map[Int, List[Int]] = list.groupBy( _ % 2)
    val groupMap2: Map[String, List[Int]] = list.groupBy( data => if (data % 2 == 0) "偶数" else "奇数")

    println(groupMap)
    println(groupMap2)

    // 给定一组词汇，按照单词的首字母进行分组
    val wordList = List("china", "america", "alice", "canada", "cary", "bob", "japan")
    println( wordList.groupBy( _.charAt(0) ) )
  }
}