from prod in products group prod by prod.Category into prodGroup where prodGroup.Any(p => p.UnitsInStock == 17) select new { Category = prodGroup.Key, Products = prodGroup }; foreach (var item in productGroups) foreach (var subitem in item.Products) Debug.WriteLine("Category:{0}--ProductName:{1}--UnitsInStock:{2}",item.Category, subitem.ProductName, subitem.UnitsInStock ); Debug.WriteLine("-----------------------------------------"); //返回所有库存都大于0的组 var productGroups2 = from prod in products group prod by prod.Category into prodGroup where prodGroup.All(p => p.UnitsInStock > 0) //判断每一个分组中是否包含库存大于0的商品,如果包含保存该结果集 select new { Category = prodGroup.Key, Products = prodGroup }; foreach (var item in productGroups) foreach (var subitem in item.Products) Debug.WriteLine("Category:{0}--ProductName:{1}--UnitsInStock:{2}", item.Category, subitem.ProductName, subitem.UnitsInStock); //对一组数字进行排序 double[] doubles = {1.7,2.3,1.9,4.1,2.9 }; var sortedDoubles = (from d in doubles orderby d descending select d).ToArray(); 记住生成字典的方法,ToDictionary var scoreRecords = new[] new {Name = "Alice", Score = 50}, new {Name = "Bob" , Score = 40}, new {Name = "Cathy", Score = 45} var scoreRecordsDict = scoreRecords.ToDictionary(sr => sr.Name); Debug.WriteLine("Bob's score: {0}", scoreRecordsDict["Bob"]); //找出单价最低的那组关口 var ret10 = from p in products group p by p.Category into g let minValue = g.Min(p => p.UnitPrice) select new Category = g.Key, CheapestProducts = g.Where(p => p.UnitPrice == minValue), Debug.WriteLine("单价最低--------------------"); foreach (var item in ret10) foreach (var subItem in item.CheapestProducts) Debug.WriteLine("Category:{0}----UnitPrice:{1}", subItem.Category, subItem.UnitPrice); Debug.WriteLine("----------------------------"); var ret11 = from p in products group p by p.Category into g select Category = g.Key, CheapestProduct = g.Min(p => p.UnitPrice), MostExpensiveProduct = g.Max(p=>p.UnitPrice), //找到最贵的商品所在的组 var ret12 = from p in products group p by p.Category into g let Max = g.Max(p => p.UnitPrice) select Category = g.Key, MostExpensiveProducts = g.Where(p => p.UnitPrice == Max), Debug.WriteLine("--------------最贵产品所在组--------------"); foreach (var item in ret12) foreach (var subItem in item.MostExpensiveProducts) Debug.WriteLine("Category:{0}----UnitPrice:{1}", subItem.Category, subItem.UnitPrice); Debug.WriteLine("----------------------------"); //use average to get average length of the worlds in the array string[] words = { "cherry", "apple", "blueberry" }; var ret13 = words.Average(w => w.Length); //use average to get average price of each category's products var ret14 = from p in products group p by p.Category into g select g.Average(p => p.UnitPrice);

  private void createLists()
            // Product data created in-memory using collection initializer:
            products =
                new List<Product> {
                    new Product { ProductID = 1, ProductName = "Chai", Category = "Beverages", UnitPrice = 18.0000M, UnitsInStock = 39 },
                    new Product { ProductID = 2, ProductName = "Chang", Category = "Beverages", UnitPrice = 19.0000M, UnitsInStock = 17 },
                    new Product { ProductID = 3, ProductName = "Aniseed Syrup", Category = "Condiments", UnitPrice = 10.0000M, UnitsInStock = 13 },
                    new Product { ProductID = 4, ProductName = "Chef Anton's Cajun Seasoning", Category = "Condiments", UnitPrice = 22.0000M, UnitsInStock = 53 },
                    new Product { ProductID = 5, ProductName = "Chef Anton's Gumbo Mix", Category = "Condiments", UnitPrice = 21.3500M, UnitsInStock = 0 },
                    new Product { ProductID = 6, ProductName = "Grandma's Boysenberry Spread", Category = "Condiments", UnitPrice = 25.0000M, UnitsInStock = 120 },
                   /* new Product { ProductID = 7, ProductName = "Uncle Bob's Organic Dried Pears", Category = "Produce", UnitPrice = 30.0000M, UnitsInStock = 15 },
                    new Product { ProductID = 8, ProductName = "Northwoods Cranberry Sauce", Category = "Condiments", UnitPrice = 40.0000M, UnitsInStock = 6 },
                    new Product { ProductID = 9, ProductName = "Mishi Kobe Niku", Category = "Meat/Poultry", UnitPrice = 97.0000M, UnitsInStock = 29 },
                    new Product { ProductID = 10, ProductName = "Ikura", Category = "Seafood", UnitPrice = 31.0000M, UnitsInStock = 31 },
                    new Product { ProductID = 11, ProductName = "Queso Cabrales", Category = "Dairy Products", UnitPrice = 21.0000M, UnitsInStock = 22 },
                    new Product { ProductID = 12, ProductName = "Queso Manchego La Pastora", Category = "Dairy Products", UnitPrice = 38.0000M, UnitsInStock = 86 },
                    new Product { ProductID = 13, ProductName = "Konbu", Category = "Seafood", UnitPrice = 6.0000M, UnitsInStock = 24 },
                    new Product { ProductID = 14, ProductName = "Tofu", Category = "Produce", UnitPrice = 23.2500M, UnitsInStock = 35 },
                    new Product { ProductID = 15, ProductName = "Genen Shouyu", Category = "Condiments", UnitPrice = 15.5000M, UnitsInStock = 39 },
                    new Product { ProductID = 16, ProductName = "Pavlova", Category = "Confections", UnitPrice = 17.4500M, UnitsInStock = 29 },
                    new Product { ProductID = 17, ProductName = "Alice Mutton", Category = "Meat/Poultry", UnitPrice = 39.0000M, UnitsInStock = 0 },
                    new Product { ProductID = 18, ProductName = "Carnarvon Tigers", Category = "Seafood", UnitPrice = 62.5000M, UnitsInStock = 42 },
                    new Product { ProductID = 19, ProductName = "Teatime Chocolate Biscuits", Category = "Confections", UnitPrice = 9.2000M, UnitsInStock = 25 },
                    new Product { ProductID = 20, ProductName = "Sir Rodney's Marmalade", Category = "Confections", UnitPrice = 81.0000M, UnitsInStock = 40 },
                    new Product { ProductID = 21, ProductName = "Sir Rodney's Scones", Category = "Confections", UnitPrice = 10.0000M, UnitsInStock = 3 },
                    new Product { ProductID = 22, ProductName = "Gustaf's Knäckebröd", Category = "Grains/Cereals", UnitPrice = 21.0000M, UnitsInStock = 104 },
                    new Product { ProductID = 23, ProductName = "Tunnbröd", Category = "Grains/Cereals", UnitPrice = 9.0000M, UnitsInStock = 61 },
                    new Product { ProductID = 24, ProductName = "Guaraná Fantástica", Category = "Beverages", UnitPrice = 4.5000M, UnitsInStock = 20 },
                    new Product { ProductID = 25, ProductName = "NuNuCa Nuß-Nougat-Creme", Category = "Confections", UnitPrice = 14.0000M, UnitsInStock = 76 },
                    new Product { ProductID = 26, ProductName = "Gumbär Gummibärchen", Category = "Confections", UnitPrice = 31.2300M, UnitsInStock = 15 },
                    new Product { ProductID = 27, ProductName = "Schoggi Schokolade", Category = "Confections", UnitPrice = 43.9000M, UnitsInStock = 49 },
                    new Product { ProductID = 28, ProductName = "Rössle Sauerkraut", Category = "Produce", UnitPrice = 45.6000M, UnitsInStock = 26 },
                    new Product { ProductID = 29, ProductName = "Thüringer Rostbratwurst", Category = "Meat/Poultry", UnitPrice = 123.7900M, UnitsInStock = 0 },
                    new Product { ProductID = 30, ProductName = "Nord-Ost Matjeshering", Category = "Seafood", UnitPrice = 25.8900M, UnitsInStock = 10 },
                    new Product { ProductID = 31, ProductName = "Gorgonzola Telino", Category = "Dairy Products", UnitPrice = 12.5000M, UnitsInStock = 0 },
                    new Product { ProductID = 32, ProductName = "Mascarpone Fabioli", Category = "Dairy Products", UnitPrice = 32.0000M, UnitsInStock = 9 },
                    new Product { ProductID = 33, ProductName = "Geitost", Category = "Dairy Products", UnitPrice = 2.5000M, UnitsInStock = 112 },
                    new Product { ProductID = 34, ProductName = "Sasquatch Ale", Category = "Beverages", UnitPrice = 14.0000M, UnitsInStock = 111 },
                    new Product { ProductID = 35, ProductName = "Steeleye Stout", Category = "Beverages", UnitPrice = 18.0000M, UnitsInStock = 20 },
                    new Product { ProductID = 36, ProductName = "Inlagd Sill", Category = "Seafood", UnitPrice = 19.0000M, UnitsInStock = 112 },
                    new Product { ProductID = 37, ProductName = "Gravad lax", Category = "Seafood", UnitPrice = 26.0000M, UnitsInStock = 11 },
                    new Product { ProductID = 38, ProductName = "Côte de Blaye", Category = "Beverages", UnitPrice = 263.5000M, UnitsInStock = 17 },
                    new Product { ProductID = 39, ProductName = "Chartreuse verte", Category = "Beverages", UnitPrice = 18.0000M, UnitsInStock = 69 },
                    new Product { ProductID = 40, ProductName = "Boston Crab Meat", Category = "Seafood", UnitPrice = 18.4000M, UnitsInStock = 123 },
                    new Product { ProductID = 41, ProductName = "Jack's New England Clam Chowder", Category = "Seafood", UnitPrice = 9.6500M, UnitsInStock = 85 },
                    new Product { ProductID = 42, ProductName = "Singaporean Hokkien Fried Mee", Category = "Grains/Cereals", UnitPrice = 14.0000M, UnitsInStock = 26 },
                    new Product { ProductID = 43, ProductName = "Ipoh Coffee", Category = "Beverages", UnitPrice = 46.0000M, UnitsInStock = 17 },
                    new Product { ProductID = 44, ProductName = "Gula Malacca", Category = "Condiments", UnitPrice = 19.4500M, UnitsInStock = 27 },
                    new Product { ProductID = 45, ProductName = "Rogede sild", Category = "Seafood", UnitPrice = 9.5000M, UnitsInStock = 5 },
                    new Product { ProductID = 46, ProductName = "Spegesild", Category = "Seafood", UnitPrice = 12.0000M, UnitsInStock = 95 },
                    new Product { ProductID = 47, ProductName = "Zaanse koeken", Category = "Confections", UnitPrice = 9.5000M, UnitsInStock = 36 },
                    new Product { ProductID = 48, ProductName = "Chocolade", Category = "Confections", UnitPrice = 12.7500M, UnitsInStock = 15 },
                    new Product { ProductID = 49, ProductName = "Maxilaku", Category = "Confections", UnitPrice = 20.0000M, UnitsInStock = 10 },
                    new Product { ProductID = 50, ProductName = "Valkoinen suklaa", Category = "Confections", UnitPrice = 16.2500M, UnitsInStock = 65 },
                    new Product { ProductID = 51, ProductName = "Manjimup Dried Apples", Category = "Produce", UnitPrice = 53.0000M, UnitsInStock = 20 },
                    new Product { ProductID = 52, ProductName = "Filo Mix", Category = "Grains/Cereals", UnitPrice = 7.0000M, UnitsInStock = 38 },
                    new Product { ProductID = 53, ProductName = "Perth Pasties", Category = "Meat/Poultry", UnitPrice = 32.8000M, UnitsInStock = 0 },
                    new Product { ProductID = 54, ProductName = "Tourtière", Category = "Meat/Poultry", UnitPrice = 7.4500M, UnitsInStock = 21 },
                    new Product { ProductID = 55, ProductName = "Pâté chinois", Category = "Meat/Poultry", UnitPrice = 24.0000M, UnitsInStock = 115 },
                    new Product { ProductID = 56, ProductName = "Gnocchi di nonna Alice", Category = "Grains/Cereals", UnitPrice = 38.0000M, UnitsInStock = 21 },
                    new Product { ProductID = 57, ProductName = "Ravioli Angelo", Category = "Grains/Cereals", UnitPrice = 19.5000M, UnitsInStock = 36 },
                    new Product { ProductID = 58, ProductName = "Escargots de Bourgogne", Category = "Seafood", UnitPrice = 13.2500M, UnitsInStock = 62 },
                    new Product { ProductID = 59, ProductName = "Raclette Courdavault", Category = "Dairy Products", UnitPrice = 55.0000M, UnitsInStock = 79 },
                    new Product { ProductID = 60, ProductName = "Camembert Pierrot", Category = "Dairy Products", UnitPrice = 34.0000M, UnitsInStock = 19 },
                    new Product { ProductID = 61, ProductName = "Sirop d'érable", Category = "Condiments", UnitPrice = 28.5000M, UnitsInStock = 113 },
                    new Product { ProductID = 62, ProductName = "Tarte au sucre", Category = "Confections", UnitPrice = 49.3000M, UnitsInStock = 17 },
                    new Product { ProductID = 63, ProductName = "Vegie-spread", Category = "Condiments", UnitPrice = 43.9000M, UnitsInStock = 24 },
                    new Product { ProductID = 64, ProductName = "Wimmers gute Semmelknödel", Category = "Grains/Cereals", UnitPrice = 33.2500M, UnitsInStock = 22 },
                    new Product { ProductID = 65, ProductName = "Louisiana Fiery Hot Pepper Sauce", Category = "Condiments", UnitPrice = 21.0500M, UnitsInStock = 76 },
                    new Product { ProductID = 66, ProductName = "Louisiana Hot Spiced Okra", Category = "Condiments", UnitPrice = 17.0000M, UnitsInStock = 4 },
                    new Product { ProductID = 67, ProductName = "Laughing Lumberjack Lager", Category = "Beverages", UnitPrice = 14.0000M, UnitsInStock = 52 },
                    new Product { ProductID = 68, ProductName = "Scottish Longbreads", Category = "Confections", UnitPrice = 12.5000M, UnitsInStock = 6 },
                    new Product { ProductID = 69, ProductName = "Gudbrandsdalsost", Category = "Dairy Products", UnitPrice = 36.0000M, UnitsInStock = 26 },
                    new Product { ProductID = 70, ProductName = "Outback Lager", Category = "Beverages", UnitPrice = 15.0000M, UnitsInStock = 15 },
                    new Product { ProductID = 71, ProductName = "Flotemysost", Category = "Dairy Products", UnitPrice = 21.5000M, UnitsInStock = 26 },
                    new Product { ProductID = 72, ProductName = "Mozzarella di Giovanni", Category = "Dairy Products", UnitPrice = 34.8000M, UnitsInStock = 14 },
                    new Product { ProductID = 73, ProductName = "Röd Kaviar", Category = "Seafood", UnitPrice = 15.0000M, UnitsInStock = 101 },
                    new Product { ProductID = 74, ProductName = "Longlife Tofu", Category = "Produce", UnitPrice = 10.0000M, UnitsInStock = 4 },
                    new Product { ProductID = 75, ProductName = "Rhönbräu Klosterbier", Category = "Beverages", UnitPrice = 7.7500M, UnitsInStock = 125 },
                    new Product { ProductID = 76, ProductName = "Lakkalikööri", Category = "Beverages", UnitPrice = 18.0000M, UnitsInStock = 57 },
                    new Product { ProductID = 77, ProductName = "Original Frankfurter grüne Soße", Category = "Condiments", UnitPrice = 13.0000M, UnitsInStock = 32 }*/
                    var productGroups =              from prod in products              group prod by prod.Category into prodGroup              where prodGroup.Any(p => p.UnitsInStock == 17)              select new {
        public string Name { set; get; }
        public int Age { set; get; }
        public string Gender { set; get; }
        public override string ToString() => Name;
创建测试数据
List<Person> personList = new List
				
LINQ 简介
语言集成查询 (LINQ) 是 Visual Studio 2008 和 .NET Framework 3.5 版中引入的一项创新功能。
传统上，针对数据的查询都是以简单的字符串表示，而没有编译时类型检查或 IntelliSense 支持。此外，您还必须针对以下各种数据源学习一种不同的查询语言：SQL 数据库、XML 文档、各种 Web 服务等等。 通过LINQ， 您可以使用语言关键字和熟悉的运算符针对强类型化对象集合编写查询。
在 Visual Studio 中，可以为以下数据源编写 L
				
这里介绍Linq使用Group By和Count得到每个CategoryID中产品的数量，Linq使用Group By和Count得到每个CategoryID中断货产品的数量等方面。
学经常会遇到Linq使用Group By问题，这里将介绍Linq使用Group By问题的解决方法。
var q =from p in db.Productsgroup p by p.Cate...
				
LINQ和Lambda都是C#编程语言的功能，但它们有不同的用途。
LINQ是一个查询语言，允许您使用类似于SQL的语法查询各种数据源，例如数据库、集合、XML文档等。使用LINQ可以更容易地查询和处理数据，从而减少了编写大量循环和条件语句的代码。
Lambda是一种表达式，用于创建匿名方法或委托。Lambda表达式通常用于LINQ查询中作为筛选器、选择器或排序器。它允许您更轻松地编写匿名函数，并且可以提高代码的可读性和可维护性。
因此，虽然LINQ和Lambda经常一起使用，但它们有不同的功能和用途。LINQ用于查询和处理数据，而Lambda用于编写匿名方法和委托。