如何在scala中聚合+ group by？

case class Employee(name: String, department: String)

val employees = List(
  Employee("Alice", "HR"),
  Employee("Bob", "IT"),
  Employee("Charlie", "HR"),
  Employee("David", "IT"),
  Employee("Eve", "HR")
)

val groupedEmployees = employees.groupBy(_.department)
val employeeCountByDepartment = groupedEmployees.mapValues(_.size)

case class Employee(name: String, department: String, salary: Double)

val employees = List(
  Employee("Alice", "HR", 50000),
  Employee("Bob", "IT", 60000),
  Employee("Charlie", "HR", 55000),
  Employee("David", "IT", 65000),
  Employee("Eve", "HR", 52000)
)

val groupedEmployees = employees.groupBy(_.department)
val averageSalaryByDepartment = groupedEmployees.mapValues { employees =>
  val totalSalary = employees.map(_.salary).sum
  val employeeCount = employees.size
  totalSalary / employeeCount
}