linq GroupBy 多字段分组
/// <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; } }
// 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); }
断点调试的结果是:
输出结果是
下面等同的linq的写法如下:
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); }
总结:多key分组是一种一维的分组,不是组内分组,多个key完全相同时,即为一组,只要有一个key不同,不为一组