6-4 Select拡張メソッド

C#のサンプル

IEnumerable(T) インターフェイスの
Select拡張メソッドのサンプルです。

メソッド構文での使用例

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

class Program
{
    static void Main()
    {
        Console.WriteLine("■■■式形式■■■");
        int[] ArrInt = { 1, 2, 3, 4 };
        var query1 = ArrInt.Select(A => new
        {
            Col1 = A * 100,
            Col2 = (A % 2 == 0).ToString(),
            Col3 = (A % 2 == 1).ToString(),
        });
        foreach (var Any in query1) Console.WriteLine(Any);

        Console.WriteLine("■■■文形式■■■");
        IEnumerable<string> query2 = Enumerable.Range(1, 6).
            Select(A =>
            {
                if (A % 3 == 0 && A % 5 == 0) return "Fizz Buzz";
                if (A % 3 == 0) return "Fizz";
                if (A % 5 == 0) return "Buzz";
                return A.ToString();
            });
        foreach (string Any in query2) Console.WriteLine(Any);

        Console.WriteLine("■■■連番を作成してくれる、select拡張メソッドのオーバーロード■■■");
        IEnumerable<string> query3 = Enumerable.Repeat("連番", 3).Select((A, rn) => A + rn);
        foreach (string Any in query3) Console.WriteLine(Any);
    }
}
//出力結果
//■■■式形式■■■
//{ Col1 = 100, Col2 = False, Col3 = True }
//{ Col1 = 200, Col2 = True, Col3 = False }
//{ Col1 = 300, Col2 = False, Col3 = True }
//{ Col1 = 400, Col2 = True, Col3 = False }
//■■■文形式■■■
//1
//2
//Fizz
//4
//Buzz
//Fizz
//■■■連番を作成してくれる、select拡張メソッドのオーバーロード■■■
//連番0
//連番1
//連番2

クエリ構文での使用例

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

class Program
{
    static void Main()
    {
        Console.WriteLine("■■■式形式■■■");
        int[] ArrInt = { 1, 2, 3, 4 };
        var query1 = from A in ArrInt
                     select (new
                            {
                                Col1 = A * 100,
                                Col2 = (A % 2 == 0).ToString(),
                                Col3 = (A % 2 == 1).ToString(),
                            });
        foreach (var Any in query1) Console.WriteLine(Any);

        Console.WriteLine("■■■文形式■■■");
        Console.WriteLine("クエリ構文では、使えないようです。");

        Console.WriteLine("■■■連番を作成してくれる、select拡張メソッドのオーバーロード■■■");
        Console.WriteLine("クエリ構文では、使えないようです。");
    }
}
//出力結果
//■■■式形式■■■
//{ Col1 = 100, Col2 = False, Col3 = True }
//{ Col1 = 200, Col2 = True, Col3 = False }
//{ Col1 = 300, Col2 = False, Col3 = True }
//{ Col1 = 400, Col2 = True, Col3 = False }

Arrayクラスでの代用案

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

class Program
{
    internal class EntitiyClass
    {
        internal int Col1;
        internal string Col2;
        internal string Col3;

        public override string ToString() //オーバーライド
        {
            return string.Format("Col1={0},Col2={1},Col3={2}", Col1, Col2, Col3);
        }
    }

    static void Main()
    {
        Console.WriteLine("■■■式形式■■■");
        int[] ArrInt = { 1, 2, 3, 4 };
        EntitiyClass[] EntitiyArr = new EntitiyClass[ArrInt.Length];

        for (int I = 0; I <= ArrInt.GetUpperBound(0); I++) {
            EntitiyArr[I] = (new EntitiyClass()
            {
                Col1 = ArrInt[I] * 100,
                Col2 = (ArrInt[I] % 2 == 0).ToString(),
                Col3 = (ArrInt[I] % 2 == 1).ToString()
            });
        }
        foreach (EntitiyClass Any in EntitiyArr) Console.WriteLine(Any);

        Console.WriteLine("■■■文形式■■■");
        int[] intQuery = Enumerable.Range(1, 6).ToArray();
        string[] stringQuery = new string[intQuery.Length];
        for (int I = 0; I <= intQuery.GetUpperBound(0); I++) {
            int currVal = intQuery[I];
            if (currVal % 3 == 0 && currVal % 5 == 0) stringQuery[I] = "Fizz Buzz";
            else if (currVal % 3 == 0) stringQuery[I] = "Fizz";
            else if (currVal % 5 == 0) stringQuery[I] = "Buzz";
            else stringQuery[I] = currVal.ToString();
        }
        foreach (string Any in stringQuery) Console.WriteLine(Any);

        Console.WriteLine("■■■連番を作成してくれる、select拡張メソッドのオーバーロード■■■");
        string[] query3 = Enumerable.Repeat("連番", 3).ToArray();
        string[] stringQuery3 = new string[query3.Length];
        for (int I = 0; I <= stringQuery3.GetUpperBound(0); I++) {
            stringQuery3[I] = query3[I] + (I + 1).ToString();
        }
        foreach (string Any in stringQuery3) Console.WriteLine(Any);
    }
}

Listジェネリックでの代用案

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

class Program
{
    internal class EntitiyClass
    {
        internal int Col1;
        internal string Col2;
        internal string Col3;

        public override string ToString() //オーバーライド
        {
            return string.Format("Col1={0},Col2={1},Col3={2}", Col1, Col2, Col3);
        }
    }

    static void Main()
    {
        Console.WriteLine("■■■式形式■■■");
        var BaseList1 = new List<int>() { 1, 2, 3, 4 };
        var ResultList1 = new List<EntitiyClass>();
        for (int I = 0; I <= BaseList1.Count-1; I++) {
            ResultList1.Add(new EntitiyClass()
            {
                Col1 = BaseList1[I] * 100,
                Col2 = (BaseList1[I] % 2 == 0).ToString(),
                Col3 = (BaseList1[I] % 2 == 1).ToString()
            });
        }
        foreach (var Any in ResultList1) Console.WriteLine(Any);

        Console.WriteLine("■■■文形式■■■");
        var BaseList2 = Enumerable.Range(1, 6).ToList();
        var ResultList2 = new List<string>();
        foreach (int Any in BaseList2) {
            if (Any % 3 == 0 && Any % 5 == 0) ResultList2.Add("Fizz Buzz");
            else if (Any % 3 == 0) ResultList2.Add("Fizz");
            else if (Any % 5 == 0) ResultList2.Add("Buzz");
            else ResultList2.Add(Any.ToString());
        }
        foreach (var Any in ResultList2) Console.WriteLine(Any);

        Console.WriteLine("■■■連番を作成してくれる、select拡張メソッドのオーバーロード■■■");
        var BaseList3 = Enumerable.Repeat("連番", 3).ToList();
        var ResultList3 = new List<string>();
        int Counter = 0;
        foreach (string Any in BaseList3)
            ResultList3.Add(Any + (Counter++));
        foreach (string Any in ResultList3) Console.WriteLine(Any);
    }
}

Dictionaryジェネリックでの代用案

作成中

DataTableクラスでの代用案

作成中

解説

作成中