Linq 和 Lambda 查询中按照多个值进行分组GroupBy

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);}

其他示例：

 【Lambda示例】            List<AddressBookPersonDto> bookPersons = (from a in addressClassPersons                                                      where a.AddressBookPerson != null                                                      select a.AddressBookPerson).ToList().MapTo<List<AddressBookPersonDto>>().GroupBy(a => new                                                        {                                                            a.Id,                                                            a.Name,                                                            a.JobTitle,                                                            a.FixedTelephone,                                                            a.MobilePhone,                                                            a.Email,                                                            a.OrganizationId                                                        })                                                    .Select(g => new AddressBookPersonDto()                                                    {                                                        Id = g.Key.Id,                                                        Name = g.Key.Name,                                                        JobTitle = g.Key.JobTitle,                                                        FixedTelephone = g.Key.FixedTelephone,                                                        MobilePhone = g.Key.MobilePhone,                                                        Email = g.Key.Email,                                                        OrganizationId = g.Key.OrganizationId,                                                        OrganizationName = g.Key?.OrganizationId > 0 ? _organizationManager.GetOrganization(g.Key.OrganizationId).DisplayName : String.Empty                                                    }).ToList();            
【Linq示例】
            List<AddressBookPersonDto> addressBookPersons = (from a in addressClassPersons                                                             where a.AddressBookPerson != null                                                             group a by new {                                                                 a.AddressBookPerson.Id,                                                                 a.AddressBookPerson.Name,                                                                 a.AddressBookPerson.JobTitle,                                                                 a.AddressBookPerson.FixedTelephone,                                                                 a.AddressBookPerson.MobilePhone,                                                                 a.AddressBookPerson.Email,                                                                 a.AddressBookPerson.OrganizationId                                                             } into g                                                            select new AddressBookPersonDto()                                                            {                                                                Id = g.Key.Id,                                                                Name = g.Key.Name,                                                                JobTitle = g.Key.JobTitle,                                                                FixedTelephone = g.Key.FixedTelephone,                                                                MobilePhone = g.Key.MobilePhone,                                                                Email = g.Key.Email,                                                                OrganizationId = g.Key.OrganizationId,                                                                OrganizationName = g.Key?.OrganizationId > 0 ? _organizationManager.GetOrganization(g.Key.OrganizationId).DisplayName : String.Empty                                                            }).ToList();