I am not able to use multiple aggregate function with multiple group by attribute using java 8 stream apis. Yet I am able to use single aggregate function with multiple group by attribute using java stream but I have a requirement where I need multiple min or max or aggregate function to use modification on list.

I need the same result that can get it from SQL like below mentioned but I have an employee list and I have to do this with java only.

Note: Employee ID is not unique its duplicate in employee table in my example.

SELECT emp_id,
       emp_name,
       year_of_joining,
       gender,
       department,
       Min(salary),
       Min(age)
FROM   employee
GROUP  BY emp_id,
          emp_name,
          year_of_joining,
          gender,
          department 

Below is the list of Employee Object

List<Employee> employeeList = new ArrayList<Employee>();
         
employeeList.add(new Employee(111, "Jiya Brein", 32, "Female", "HR", 2011, 25000.0));
employeeList.add(new Employee(111, "Jiya Brein", 32, "Female", "HR", 2011, 21000.0));
employeeList.add(new Employee(111, "Jiya Brein", 32, "Female", "HR", 2011, 29000.0));
employeeList.add(new Employee(111, "Jiya Brein", 15, "Female", "HR", 2011, 25000.0));

Below is the Employee Object

class Employee
{
    int id;
     
    String name;
     
    int age;
     
    String gender;
     
    String department;
     
    int yearOfJoining;
     
    double salary;
     
    public Employee(int id, String name, int age, String gender, String department, int yearOfJoining, double salary) 
    {
        this.id = id;
        this.name = name;
        this.age = age;
        this.gender = gender;
        this.department = department;
        this.yearOfJoining = yearOfJoining;
        this.salary = salary;
    }
     
    public int getId() 
    {
        return id;
    }
     
    public String getName() 
    {
        return name;
    }
     
    public int getAge() 
    {
        return age;
    }
     
    public String getGender() 
    {
        return gender;
    }
     
    public String getDepartment() 
    {
        return department;
    }
     
    public int getYearOfJoining() 
    {
        return yearOfJoining;
    }
     
    public double getSalary() 
    {
        return salary;
    }
     
    @Override
    public String toString() 
    {
        return "Id : " id
                 ", Name : " name
                 ", age : " age
                 ", Gender : " gender
                 ", Department : " department
                 ", Year Of Joining : " yearOfJoining
                 ", Salary : " salary;
    }
}

I have tried lot but I was not able to get the exact result with Employee Object. Any Help would be really appreciated. I don't know how to use multiple aggregate function with multiple group by statements so that in last I can get list of Employee object. I have tried to do this with below mentioned code but able to do with single aggregate. How can i do with multiple aggregate.

    Function<Employee, List<Object>> compositeKey = personRecord -> Arrays.<Object>asList(personRecord.getId(),
        personRecord.getName(), personRecord.getGender(), personRecord.getDepartment(),
        personRecord.getYearOfJoining());

    Map<List<Object>, Optional<Employee>> collect = employeeList.stream().collect(
        Collectors.groupingBy(compositeKey, Collectors.minBy(Comparator.comparingDouble(Employee::getSalary))));

CodePudding user response：

Here is the solution.

Function<Employee, List<Object>> compositeKey = personRecord -> Arrays.<Object>asList(personRecord.getId(),
        personRecord.getName(), personRecord.getGender(), personRecord.getDepartment(),
        personRecord.getYearOfJoining());

 List<Employee> groupedEmployees = employeeList.stream().collect(Collectors.groupingBy(compositeKey)).values()
            .stream()
            .map(e -> new Employee(e.get(0).getId(), e.get(0).getName(),
                e.stream().mapToInt(Employee::getAge).min().orElse(0), e.get(0).getGender(), e.get(0).getDepartment(),
                e.get(0).getYearOfJoining(), e.stream().mapToDouble(Employee::getSalary).min().orElse(0)))
            .collect(Collectors.toList());

CodePudding user response：

Here a dangerous solution

override Employee equals and HashCode methods like below(you can add null check if u need)

 @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Employee employee = (Employee) o;
        return id == employee.id && yearOfJoining == employee.yearOfJoining && name.equals(employee.name) && gender.equals(employee.gender) && department.equals(employee.department);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, name, gender, department, yearOfJoining);
    }

now u can group like that

final Map<Employee, List<Double>> groupedEmployees = employeeList.stream()
                .collect(Collectors.groupingBy(e -> e,
                        Collectors.collectingAndThen(Collectors.toList(), list -> {
                            final double minSalary = list.stream().mapToDouble(Employee::getSalary).min().orElse(0);
                            final double minAge = list.stream().mapToDouble(Employee::getAge).min().orElse(0);
                            return List.of(minSalary, minAge);
                        })));

for test add more data coz your data doesn't contain same group (do it before mapping :) )

employeeList.add(new Employee(111, "Jiya Brein", 32, "Female", "HR", 2011, 25000.0));
employeeList.add(new Employee(111, "Jiya Brein", 32, "Female", "HR", 2011, 21000.0));
employeeList.add(new Employee(111, "Jiya Brein", 32, "Female", "HR", 2011, 29000.0));
employeeList.add(new Employee(111, "Jiya Brein", 15, "Female", "HR", 2011, 25000.0));

groupedEmployees.forEach((k, v) -> System.out.println(k   " -> "   v));