java - 我如何使用计数处理ArrayList，并按函数分组，并在值中包含字符串数组

Question

我正在处理员工的数组列表，需要按员工数量按函数使用情况进行分组，计算活跃员工和非活跃员工。我知道如何处理总数，但是当值位于数组字符串中时，即一名员工与多个部门关联时，如何使用按函数分组处理数组列表。

public class Employee {
    private String name;
    private List<String> department;
    private String status;
    public Employee(String name, List<String> department, String status) {
        this.setName(name);
        this.setDepartment(department);
        this.setStatus(status);
    }
    public String getName() {
        return name;
    }
    public List<String> getDepartment() {
        return department;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void setDepartment(List<String> department) {
        this.department = department;
    }
    public String getStatus() {
        return status;
    }
    public void setStatus(String status) {
        this.status = status;
    }
}

ArrayList<Employee> listEmployee = new ArrayList<Employee>();

         List<String> listString1 = Arrays.asList("IT", "Sales");
         List<String> listString2 = Arrays.asList("Sales");
         List<String> listString3 = Arrays.asList("Sales");


         listEmployee.add(new Employee("Ravi", listString1, "active"));
         listEmployee.add(new Employee("Tom", listString2, "inactive"));
         listEmployee.add(new Employee("Kanna", listString3, "inactive"));

int count = 0;
for (Employee e : listEmployee) {
    count++;
}
System.out.println("Count of Employees" + count);

这是我试图获取员工数量的上述代码

int count = 0;
for (Employee e : listEmployee) {
    count++;
}
System.out.println("Count of Employees" + count);

请帮我按部门分组处理数据

我期待以下输出:

Department total activeCount inactiveCount
IT         1     1           0
Sales      3     1           2

Answer 1

首先我们需要创建一个类来保存每个部门的计数器。
类似于下面的预兆(为了简洁起见，实例变量被设为公共(public))。需要 equals() 和 hashCode() 因为我们要将此类的实例放入 Map

public class DepartmentStats {
    public String name;
    public int total = 0;
    public int activeCount = 0;
    public int inactiveCount = 0;

    public DepartmentStats() {}
    public DepartmentStats(String name) {
        this.name = name;
    }

    /**
     * equality based on dept name
     */
    @Override
    public boolean equals(Object other) {
        return other instanceof DepartmentStats && 
               this.name.equals(((DepartmentStats) other).name);
    }

    /**
     * hash code based on dept name
     */
    @Override
    public int hashCode() {
        return name.hashCode();
    }
}

其次，我们将创建一个 map ，允许我们按部门对员工进行分组并保存累积计数器

Map<String, DepartmentStats> departmentStatsMap = new HashMap<>();

现在，迭代员工列表是一个简单的问题，对于每个项目，迭代部门列表，从 map 中获取适当的条目并累积计数器(并放回到 map 中):

for (Employee employee : listEmployee) {
    for (String departmentName : employee.getDepartment()) {
        DepartmentStats departmentStats = departmentStatsMap.get(departmentName);
        if (departmentStats == null) departmentStats = new DepartmentStats(departmentName);
        departmentStats.total++;
        if (employee.getStatus().equals("active")) departmentStats.activeCount++;
        if (employee.getStatus().equals("inactive")) departmentStats.inactiveCount++;
        departmentStatsMap.put(departmentName, departmentStats);
    }
}