java8stream操作：将集合根据元素的某个属性分组求统计数据

た入场券 2022-04-15 06:06 1383阅读 0赞

student类：

public class Student {
    
        private int id;
        private String name;
        private int score;
    
        public Student(int id, String name, int score) {
            this.id = id;
            this.name = name;
            this.score = score;
        }
    get...
    set...
    }

求统计数据：

List<Student> students = new ArrayList<>();
    
            students.add(new Student(1,"张三",90));
            students.add(new Student(1,"张三",83));
            students.add(new Student(1,"张三",79));
            students.add(new Student(2,"李四",60));
            students.add(new Student(3,"王五",30));
            students.add(new Student(3,"王五",70));
            students.add(new Student(3,"王五",75));
            students.add(new Student(4,"赵六",60));
            students.add(new Student(4,"赵六",85));
            
            Map<Integer, IntSummaryStatistics> collect = students.stream().collect(Collectors.groupingBy(Student::getId, Collectors.summarizingInt(Student::getScore)));
            System.out.println(collect);

上面代码根据id求score的统计数据(求和，个数，平均数，最大最小值)，结果如下：

{1=IntSummaryStatistics{count=3, sum=252, min=79, average=84.000000, max=90}, 2=IntSummaryStatistics{count=1, sum=60, min=60, average=60.000000, max=60}, 3=IntSummaryStatistics{count=3, sum=175, min=30, average=58.333333, max=75}, 4=IntSummaryStatistics{count=2, sum=145, min=60, average=72.500000, max=85}}

也可以只求和：

Map<Integer, Integer> collect1 = students.stream().collect(Collectors.groupingBy(Student::getId, Collectors.summingInt(Student::getScore)));

运行结果

{1=252, 2=60, 3=175, 4=145}