List中常用的linq操作

 [Serializable]
    public class Product
    {
        public Product()
        {
          
        
        }

        public Product(string id,string pname,int num,double price)
        {
            this.ProductID = id;
            this.ProductName = pname;
            this.Num = num;
            this.Price = price;
        }
        public string ProductID { get; set; }
        public string ProductName { get; set; }
        public int Num { get; set; }
        public double Price { get; set; }
   

    }

初始化

List<Product> plist = new List<Product>()
            {
                new Product{ ProductID="01",ProductName ="牛奶",Num=45,Price=4.0 },
                new Product{ ProductID="02",ProductName ="饼干",Num=8,Price=8.5 },
                new Product{ ProductID="03",ProductName ="糖果",Num=9,Price=2.1 },
                new Product{ ProductID="04",ProductName ="饮料",Num=10,Price=3.5 },
            };

1.使用linq获取list集合中的某个字段值的集合

double[] Prices = plist.Select(u => u.Price).ToArray();

2.使用linq求list集合中所有对象price字段的和

var Price_sum = plist.Sum(u => u.Price)

求数量*单价的和

var Price_sum = plist.Sum(u => u.Price*u.Num)