Linq-grouping-operators

LINQでの演算子のグループ化

オペレーターは、共通の共有属性に基づいていくつかのグループにデータを入れます。

Operator	Description	C# Query Expression Syntax	VB Query Expression Syntax
GroupBy	Organize a sequence of items in groups and return them as an IEnumerable collection of type IGrouping<key, element>	group … by -or- group … by … into …	Group … By … Into …
ToLookup	Execute a grouping operation in which a sequence of key pairs are returned	Not Applicable	Not Applicable

GroupByの例-クエリ式

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

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

         List<int> numbers = new List<int>() { 35, 44, 200, 84, 3987, 4, 199, 329, 446, 208 };

         IEnumerable<IGrouping<int, int>> query = from number in numbers
                                      group number by number % 2;

         foreach (var group in query) {
            Console.WriteLine(group.Key == 0 ? "\nEven numbers:" : "\nOdd numbers:");

            foreach (int i in group)
               Console.WriteLine(i);
         }

         Console.ReadLine();
      }
   }
}

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VB

Module Module1
   Sub Main()
      Dim numbers As New System.Collections.Generic.List(Of Integer)(
      New Integer() {35, 44, 200, 84, 3987, 4, 199, 329, 446, 208})

      Dim query = From number In numbers
                  Group By Remainder = (number Mod 2) Into Group

      For Each group In query
         Console.WriteLine(If(group.Remainder = 0, vbCrLf &"Even numbers:", vbCrLf &"Odd numbers:"))

         For Each num In group.Group
            Console.WriteLine(num)
         Next

      Next

      Console.ReadLine()

   End Sub

End Module

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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-

Odd numbers:
35
3987
199
329

Even numbers:
44
200
84
4
446
208

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