java 8 groupingBy列表列表

Question

假设我们有一个对象Draw:

class Draw {

private int num1, num2, num3;

public Draw (int num1, int num2, int num3) {
    this.num1 = num1;
    this.num2 = num2;
    this.num3 = num3;
}

public int getNum1() {
    return num1;
}

public void setNum1(int num1) {
    this.num1 = num1;
}

public int getNum2() {
    return num2;
}

public void setNum2(int num2) {
    this.num2 = num2;
}

public int getNum3() {
    return num3;
}

public void setNum3(int num3) {
    this.num3 = num3;
}

public List<Integer> getResultAsList() {
    return Arrays.asList(num1, num2, num3);
}

}

现在,有了绘制列表,我需要得到一个Map,其中key是绘制中的数字,value是一个计数(绘制该数字的次数)

例如,拥有

List<Draw> drawList = Arrays.asList(new Draw(1,2,5), new Draw(1,5,6));

我想获得如下地图:{1 = 2,2 = 1,5 = 2,6 = 1}

我可以使用java 8的新groupingBy操作或其他新功能来实现吗？

谢谢.

Answer 1

如果我一切都正确的话：

Map<Integer, Long> map = drawList
      .stream()
      .flatMap(x -> Stream.of(x.getNum1(), x.getNum2(), x.getNum3()))
      .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

System.out.println(map); // {1=2, 2=1, 5=2, 6=1}

或者显然是这样的：

Map<Integer, Long> map2 = drawList
            .stream()
            .flatMap(x -> x.getResultAsList().stream())
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));