using System;

using System.Diagnostics;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var count = 60000;

        var stopwatch = Stopwatch.StartNew();

        var elements = Enumerable.Range(1, count).Select(i => (i, $"Item #{i}")).ToArray();

        var elements2 = Enumerable.Range(1, count).Select(i => (i, $"SECRETS #{i}")).Reverse().ToArray();

​

        stopwatch.Stop();

        Console.WriteLine($"{stopwatch.Elapsed} to generate collection");

        Console.WriteLine();

​

        stopwatch = Stopwatch.StartNew();

        var found1 = elements.Select(e => elements2.FirstOrDefault(x => x.Item1 == e.Item1));

        stopwatch.Stop();

        Console.WriteLine($"{stopwatch.Elapsed} to find with FirstOrDefault");

        Console.WriteLine();

​

        stopwatch = Stopwatch.StartNew();

        var dictionary = elements2.ToDictionary(e => e.Item1, e => e.Item2);

        stopwatch.Stop();

        Console.WriteLine($"{stopwatch.Elapsed} to build dictionary");

​

        stopwatch = Stopwatch.StartNew();

        var found2 = elements.Select(e => dictionary[e.Item1]);

        stopwatch.Stop();

        Console.WriteLine($"{stopwatch.Elapsed} to find with dictionary indexing");

        stopwatch = Stopwatch.StartNew();

        var found3 = 

        from e in elements

        join e2 in elements2 on e.Item1 equals e2.Item1 into grouped

        select (e.Item1, grouped.FirstOrDefault());

        stopwatch.Stop();

        Console.WriteLine($"{stopwatch.Elapsed} with query");

        Console.WriteLine(found3.Count());

        Console.WriteLine(found3.FirstOrDefault());

​

    }

}

​