Linq-conversions

LINQでの変換

演算子は入力オブジェクトのタイプを変更し、さまざまなアプリケーションで使用されます。

Operator	Description	C# Query Expression Syntax	VB Query Expression Syntax
AsEnumerable	Returns the input typed as IEnumerable<T>	Not Applicable	Not Applicable
AsQueryable	A (generic) IEnumerable is converted to a (generic) IQueryable	Not Applicable	Not Applicable
Cast	Performs casting of elements of a collection to a specified type	Use an explicitly typed range variable. Eg:from string str in words	From … As …
OfType	Filters values on basis of their , depending on their capability to be cast to a particular type	Not Applicable	Not Applicable
ToArray	Forces query execution and does conversion of a collection to an array	Not Applicable	Not Applicable
ToDictionary	On basis of a key selector function set elements into a Dictionary<TKey, TValue> and forces execution of a LINQ query	Not Applicable	Not Applicable
ToList	Forces execution of a query by converting a collection to a List<T>	Not Applicable	Not Applicable
ToLookup	Forces execution of a query and put elements into a Lookup<TKey, TElement> on basis of a key selector function	Not Applicable	Not Applicable

キャストの例-クエリ式

C#

using System;
using System.Linq;

namespace Operators {
   class Cast {
      static void Main(string[] args) {

         Plant[] plants = new Plant[] {new CarnivorousPlant { Name = "Venus Fly Trap", TrapType = "Snap Trap" },
                          new CarnivorousPlant { Name = "Pitcher Plant", TrapType = "Pitfall Trap" },
                          new CarnivorousPlant { Name = "Sundew", TrapType = "Flypaper Trap" },
                          new CarnivorousPlant { Name = "Waterwheel Plant", TrapType = "Snap Trap" }};

         var query = from CarnivorousPlant cPlant in plants
                     where cPlant.TrapType == "Snap Trap"
                     select cPlant;

         foreach (var e in query) {
            Console.WriteLine("Name = {0} , Trap Type = {1}", e.Name, e.TrapType);
         }

         Console.WriteLine("\nPress any key to continue.");
         Console.ReadKey();
      }
   }

   class Plant {
      public string Name { get; set; }
   }

   class CarnivorousPlant : Plant {
      public string TrapType { get; set; }
   }
}

VB

Module Module1
   Sub Main()

      Dim plants() As Plant = {New CarnivorousPlant With {.Name = "Venus Fly Trap", .TrapType = "Snap Trap"},
                              New CarnivorousPlant With {.Name = "Pitcher Plant", .TrapType = "Pitfall Trap"},
                              New CarnivorousPlant With {.Name = "Sundew", .TrapType = "Flypaper Trap"},
                              New CarnivorousPlant With {.Name = "Waterwheel Plant", .TrapType = "Snap Trap"}}

      Dim list = From cPlant As CarnivorousPlant In plants
                 Where cPlant.TrapType = "Snap Trap"
                 Select cPlant

      For Each e In list
         Console.WriteLine("Name = {0} , Trap Type = {1}", e.Name, e.TrapType)
      Next

      Console.WriteLine(vbLf & "Press any key to continue.")
      Console.ReadKey()
   End Sub

   Class Plant
      Public Property Name As String
   End Class

   Class CarnivorousPlant
      Inherits Plant
      Public Property TrapType As String
   End Class

End Module

C＃またはVBの上記のコードがコンパイルされて実行されると、次の結果が生成されます-

Name = Venus Fly Trap, TrapType = Snap Trap
Name = Waterwheel Plant, TrapType = Snap Trap

Press any key to continue.