using System;

using System.Collections.Generic;

using System.Linq;

using System.Diagnostics;

​

public class Program

{

    public static void Main()

    {

        IEnumerable<Item> items = Enumerable.Range(0,100).Select(a=> new Item(a));

        // sorting randomly

        items = items.OrderBy( x=> new Guid()).ToList();

        var items2 = items.OrderBy( x=> new Guid()).ToList();

        int n = 5;

        Func<Item,bool> filter = x => x.Size == n;

        Run("First", () => {

            items.First( filter );

            items2.First( filter );

        });

        Run("Where First", () => {

            items.Where( filter ).First();

            items2.Where( filter ).First();

        });

        filter = x => x.Size < n;

        Run("First", () => {

            items.First( filter );

            items2.First( filter );

        });

        Run("Where First", () => {

            items.Where( filter ).First();

            items2.Where( filter ).First();

        });

        filter = x => x.Size > n;

        Run("First", () => {

            items.First( filter );

            items2.First( filter );

        });

        Run("Where First", () => {

            items.Where( filter ).First();

            items2.Where( filter ).First();

        });

    }

    public class Item{

        public String Name{ get;set; }

        public int Size {get;set;}

        public Item(int n){

            Size = n;

            Name = "a" + Size;

        }

    }

    public static void Run(String title, Action action){

        Stopwatch watch = Stopwatch.StartNew();

        for(int i=0;i<10000;i++){

            action();

        }

        watch.Stop();

        Console.WriteLine("{0} milliseconds for {1}", watch.ElapsedMilliseconds, title);

    }

}

​

​

​