Linq 中按照多个值进行分组(GroupBy)

/// <summary>要查询的对象</summary>

class Employee {

   public int ID { get;set; }

   public string FName { get; set; }

   public int Age { get; set; }

   public char Sex { get; set; }

}

如果对这个类的Age和Sex的连个字段进行分组，方法如下：

// 先造一些数据

List<Employee> empList = new List<Employee>();

empList.Add(new Employee() {

   ID = 1, FName = "John", Age = 23, Sex = 'M'

});

empList.Add(new Employee() {

   ID = 2, FName = "Mary", Age = 25, Sex = 'F'

});



empList.Add(new Employee() {

   ID = 3, FName = "Amber", Age = 23, Sex = 'M'

});

empList.Add(new Employee() {

   ID = 4, FName = "Kathy", Age = 25, Sex = 'M'

});

empList.Add(new Employee() {

   ID = 5, FName = "Lena", Age = 27, Sex = 'F'

});



empList.Add(new Employee() {

   ID = 6, FName = "Bill", Age = 28, Sex = 'M'

});



empList.Add(new Employee() {

   ID = 7, FName = "Celina", Age = 27, Sex = 'F'

});

empList.Add(new Employee() {

   ID = 8, FName = "John", Age = 28, Sex = 'M'

});

接下来的做法是：

// 实现多key分组的扩展函数版本

var sums = empList

         .GroupBy(x => new { x.Age, x.Sex })

         .Select(group => new {

            Peo = group.Key, Count = group.Count()

         });

foreach (var employee in sums) {

   Console.WriteLine(employee.Count + ": " + employee.Peo);

}



// 实现多key分组的lambda版本

var sums2 = from emp in empList

            group emp by new { emp.Age, emp.Sex } into g

            select new { Peo = g.Key, Count = g.Count() };

foreach (var employee in sums) {

   Console.WriteLine(employee.Count + ": " + employee.Peo);

}

这个例子中就充分利用了匿名类型