C#中如何使用order by、group by？

Order by is used to sort the arrays in the ascending or in the descending order

GroupBy operator belong to Grouping Operators category. This operator takes a flat sequence of items, organize that sequence into groups (IGrouping<K,V>) based on a specific key and return groups of sequence

Example

class ElectronicGoods {
   public int Id { get; set; }
   public string Name { get; set; }
   public string Category { get; set; }
   public static List<ElectronicGoods> GetElectronicItems() {
      return new List<ElectronicGoods>() {
         new ElectronicGoods { Id = 1, Name = "Mobile", Category = "Phone"},
         new ElectronicGoods { Id = 2, Name = "LandLine", Category = "Phone"},
         new ElectronicGoods { Id = 3, Name = "Television", Category = "TV"},
         new ElectronicGoods { Id = 4, Name = "Grinder", Category = "Food"},
         new ElectronicGoods { Id = 5, Name = "Mixer", Category = "Food"},
      };
   }
}
class Program {
   static void Main() {
      //Group by
      var res=ElectronicGoods.GetElectronicItems().GroupBy(x => x.Category).Select(x => new {
         Key = x.Key,
         electronicGoods = x.OrderBy(c => c.Name)
      });
      foreach (var group in res) {
         Console.WriteLine("{0} - {1}", group.Key, group.electronicGoods.Count());
         Console.WriteLine("----------");
         foreach (var electronicGoods in group.electronicGoods) {
            Console.WriteLine(electronicGoods.Name + "\t" + electronicGoods.Category);
         }
         Console.WriteLine(); Console.WriteLine();
      }
      Console.ReadKey();
   }
}

Output

Phone - 2
----------
LandLine Phone
Mobile Phone
TV - 1
----------
Television TV
Food - 2
----------
Grinder Food
Mixer Food

Order By

的翻译为：

按顺序排列

class ElectronicGoods {
   public int Id { get; set; }
   public string Name { get; set; }
   public string Category { get; set; }
   public static List<ElectronicGoods> GetElectronicItems() {
      return new List<ElectronicGoods>() {
         new ElectronicGoods { Id = 1, Name = "Mobile", Category = "Phone"},
         new ElectronicGoods { Id = 2, Name = "LandLine", Category = "Phone"},
         new ElectronicGoods { Id = 3, Name = "Television", Category = "TV"},
         new ElectronicGoods { Id = 4, Name = "Grinder", Category = "Food"},
         new ElectronicGoods { Id = 5, Name = "Mixer", Category = "Food"},
      };
   }
}
class Program {
   static void Main() {
      //Order by
      var res = ElectronicGoods.GetElectronicItems().OrderBy(x => x.Category);
      foreach (var items in res) {
         Console.WriteLine(items.Name + "\t" + items.Category);
      }
      Console.ReadKey();
   }
}

Output

Grinder Food
Mixer Food
Mobile Phone
LandLine Phone
Television TV

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