创建要查询的对象：
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Linq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);
}