1 package chapter07
 2 
 3 object Test14_HighLevelFunction_Map {
 4   def main(args: Array[String]): Unit = {
 5     val list = List(1,2,3,4,5,6,7,8,9)
 6 
 7     // 1. 过滤
 8     // 选取偶数
 9     val evenList = list.filter( (elem: Int) => {elem % 2 == 0} )
10     println(evenList)
11 
12     // 选取奇数
13     println(list.filter( _ % 2 == 1 ))
14 
15     println("=======================")
16 
17     // 2. 映射map
18     // 把集合中每个数乘2
19     println(list.map(_ * 2))
20     println(list.map( x => x * x))
21 
22     println("=======================")
23 
24     // 3. 扁平化
25     val nestedList: List[List[Int]] = List(List(1,2,3),List(4,5),List(6,7,8,9))
26 
27     val flatList = nestedList(0) ::: nestedList(1) ::: nestedList(2)
28     println(flatList)
29 
30     val flatList2 = nestedList.flatten
31     println(flatList2)
32 
33     println("=======================")
34 
35     // 4. 扁平映射
36     // 将一组字符串进行分词，并保存成单词的列表
37     val strings: List[String] = List("hello world", "hello scala", "hello java", "we study")
38     val splitList: List[Array[String]] = strings.map( _.split(" ") )    // 分词
39     val flattenList = splitList.flatten    // 打散扁平化
40 
41     println(flattenList)
42 
43     val flatmapList = strings.flatMap(_.split(" "))
44     println(flatmapList)
45 
46     println("========================")
47 
48     // 5. 分组groupBy
49     // 分成奇偶两组
50     val groupMap: Map[Int, List[Int]] = list.groupBy( _ % 2)
51     val groupMap2: Map[String, List[Int]] = list.groupBy( data => if (data % 2 == 0) "偶数" else "奇数")
52 
53     println(groupMap)
54     println(groupMap2)
55 
56     // 给定一组词汇，按照单词的首字母进行分组
57     val wordList = List("china", "america", "alice", "canada", "cary", "bob", "japan")
58     println( wordList.groupBy( _.charAt(0) ) )
59   }
60