Stream流中的groupingBy分组操作

 code:

//根据医院编号，查询医院所有科室信息 Department departmentQuery = new Department(); departmentQuery.setHoscode(hoscode); Example example = Example.of(departmentQuery); //所有科室列表 departmentList List departmentList = departmentRepository.findAll(example); //根据大科室编号 bigcode 分组，获取每个大科室里面下级子科室 Map> deparmentMap = departmentList.stream().collect(Collectors.groupingBy(Department::getBigcode));

partitioningBy:该函数只能返回两个集合  一个是false,一个是true

Map> part = personList.stream().collect(Collectors.partitioningBy(x -> x.getSalary() > 8000));

groupingBy:该函数返回每个分组下的所有集合数据

Map> group = personList.stream().collect(Collectors.groupingBy(Person::getSex));

4.附录所有代码 

 code:

package com.itheima.demo18_扩展字符串排序;import java.util.*;import java.util.stream.Collectors;public class Harbor {    public static void main(String[] args) {        List personList = new ArrayList();        personList.add(new Person("Tom", 8900, 28,"male", "New York"));        personList.add(new Person("Jack", 7000, 29,"male", "Washington"));        personList.add(new Person("Lily", 7800, 320,"female", "Washington"));        personList.add(new Person("Anni", 8200, 26,"female", "New York"));        personList.add(new Person("Owen", 9500, 27,"male", "New York"));        personList.add(new Person("Alisa", 7900, 29,"female", "New York"));        // 将员工按薪资是否高于8000分组        Map> part = personList.stream().collect(Collectors.partitioningBy(x -> x.getSalary() > 8000));        // 将员工按性别分组        Map> group = personList.stream().collect(Collectors.groupingBy(Person::getSex));        List female = group.get("female");        // 将员工先按性别分组，再按地区分组        Map>> group2 = personList.stream().collect(Collectors.groupingBy(Person::getSex, Collectors.groupingBy(Person::getArea)));        System.out.println("员工按薪资是否大于8000分组情况：" + part);        System.out.println("员工按性别分组情况：" + group);        System.out.println("员工按性别、地区：" + group2);    }}

6.javabean

package com.itheima.demo18_扩展字符串排序;import java.util.Objects;public class Person {    private String name; // 姓名    private int salary; // 薪资    private int age; // 年龄    private String sex; //性别    private String area; // 地区    public String getName() {        return name;    }    @Override    public boolean equals(Object o) {        if (this == o) return true;        if (o == null || getClass() != o.getClass()) return false;        Person person = (Person) o;        return salary == person.salary &&                age == person.age &&                Objects.equals(name, person.name) &&                Objects.equals(sex, person.sex) &&                Objects.equals(area, person.area);    }    @Override    public int hashCode() {        return Objects.hash(name, salary, age, sex, area);    }    @Override    public String toString() {        return "Person{" +                "name='" + name + '\'' +                ", salary=" + salary +                ", age=" + age +                ", sex='" + sex + '\'' +                ", area='" + area + '\'' +                '}';    }    public void setName(String name) {        this.name = name;    }    public int getSalary() {        return salary;    }    public void setSalary(int salary) {        this.salary = salary;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getSex() {        return sex;    }    public void setSex(String sex) {        this.sex = sex;    }    public String getArea() {        return area;    }    public void setArea(String area) {        this.area = area;    }    // 构造方法    public Person(String name, int salary, int age,String sex,String area) {        this.name = name;        this.salary = salary;        this.age = age;        this.sex = sex;        this.area = area;    }}

来源地址：https://blog.csdn.net/weixin_61503139/article/details/126074858