列表类别及其使用Lambda或经典表达式的LinQ产品的数量

Question

我需要使用LinQ lambda或经典表达式列出属于每个类别的产品的类别和计数。

这是班级：

  class Product
    {
        public int ProductID { get; set; }
        public string ProductName { get; set; }
        public string Category { get; set; }
        public decimal UnitPrice { get; set; }
        public int UnitsInStock { get; set; }
    }

这是我用来确定列表外观的列表。

  IEnumerable<Product> productList = 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",......and so on..

我有一个返回名为listProd的列表的方法。 例如，我能够在＆＃34; Beverages＆＃34;中获得产品数量。单独的类别，但这样我必须创建尽可能多的查询类别...（不好）..

int query = listProd.Where(p => p.Category == "Beverages").Count();

所以我想要的是创建这样的查询：

类别，计数（属于该类别的产品）

饮料，5

调味品，7

Answer 1

您可以使用此LINQ查询

 var result = productList.GroupBy(x => x.Category)
                         .Select(y => new { Category = y.Key, Count = y.Count() });

按类别分组，然后使用Key和Count()获取结果对象。

根据您提供的样本数据，结果将如下所示

如果您想获得有关LINQ的更多信息和示例，我建议101 LINQ Samples。

修改

根据您的评论：

您可以使用Where语句仅获取包含4个以上产品的类别。

var result = productList.GroupBy(x => x.Category)
                        .Where(x => x.Count() > 4)
                        .Select(y => new { Category = y.Key, Count = y.Count() });= y.Count() });

Answer 2

使用以下和平代码

  IEnumerable<Product> productList = 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"}


    };
        var list = (from x in productList
                    group x.Category by x.Category into g
                    select new { Category = g.Key, Count = g.Count() });