Linq-聚合函数

1.Max 获取最大值#

// 获取 Id>6的人群中的最高工资
double a = list.Where(it => it.Id > 5).Max(it => it.Salary) ;

string b = list.Max(it => it,Name);

根据Func(有返回值的委托)，返回值是什么类型，前面就用什么类型的变量去接收

2.Average 获取平均值#

//取年龄>30岁的平均工资
double a = list.Where(it => it.Age >= 30).Average(it => it.Salary)

3.Min 最小值#

4.Sum 求和#

item.Sum(it => it.Salary);

5.Count 总数#

list.Count();

6.GroupBy 分组#

class Program
    {
        static void Main(string[] args)
        {
            List<Employee> list = new()
            {
                new Employee { Id = 1, Name = "Hpf", Age = 38, Gender = true, Salary 
= 1000 },
                new Employee { Id = 2, Name = "Jim", Age = 15, Gender = true, Salary 
= 2000 },
                new Employee { Id = 3, Name = "Lily", Age = 27, Gender = false, 
Salary = 1500 },
                new Employee { Id = 4, Name = "Kimi", Age = 15, Gender = true, 
Salary = 2700 },
                new Employee { Id = 5, Name = "Nancy", Age = 38, Gender = false, 
Salary = 3200 },
                new Employee { Id = 6, Name = "Jack", Age = 21, Gender = false, 
Salary = 4400 },
                new Employee { Id = 7, Name = "Zack", Age = 38, Gender = true, 
Salary = 7500 }
            };


            IEnumerable<IGrouping<int, Employee>> items = list.GroupBy(it => 
it.Age);
            foreach (IGrouping<int, Employee> item in items)
            {
                Console.WriteLine(item.Key);
                Console.WriteLine($"最大工资：{item.Max(it => it.Salary)}");
                foreach (Employee e in item)
                {
                    Console.WriteLine(e);
                }
                Console.WriteLine("*****************");
            }
            Console.ReadLine();
        }
    }
    
    
    
    
    public class Employee
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
        public bool Gender { get; set; }
        public double Salary { get; set; }

        public override string ToString()
        {
            return $"Id={Id},Name={Name},Age={Age},Gender={Gender},Salary={Salary}";
        }
    }