Linq 和 Lambda 查询中按照多个值进行分组GroupBy

最新推荐文章于 2023-12-09 00:53:37 发布

转载最新推荐文章于 2023-12-09 00:53:37 发布 · 929 阅读

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CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/teng-0802/p/9055779.html

文章标签：

#c#

本文介绍了如何使用C#的Linq来实现对员工对象列表按照年龄和性别两个字段进行分组查询，并提供了两种实现方式：一种是通过Linq扩展方法GroupBy，另一种是使用Linq查询语法。

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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);
}

转载于:https://www.cnblogs.com/teng-0802/p/9055779.html