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="",ProductName ="牛奶",Num=,Price=4.0 },
                 new Product{ ProductID="",ProductName ="饼干",Num=,Price=8.5 },
                 new Product{ ProductID="",ProductName ="糖果",Num=,Price=2.1 },
                 new Product{ ProductID="",ProductName ="饮料",Num=,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)