linqGroupBy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() {
groupby分组
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

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