C# FindAll VS Where Speed

Question

Anyone know any speed differences between Where and FindAll on List. I know Where is part of IEnumerable and FindAll is part of List, I\'m just curious what\'s faster.

Answer 1

FindAll is obviously slower than Where, because it needs to create a new list.

Anyway, I think you really should consider Jon Hanna comment - you'll probably need to do some operations on your results and list would be more useful than IEnumerable in many cases.

I wrote small test, just paste it in Console App project. It measures time/ticks of: function execution, operations on results collection(to get perf. of 'real' usage, and to be sure that compiler won't optimize unused data etc. - I'm new to C# and don't know how it works yet,sorry).

Notice: every measured function except WhereIENumerable() creates new List of elements. I might be doing something wrong, but clearly iterating IEnumerable takes much more time than iterating list.

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

namespace Tests
{

    public class Dummy
    {
        public int Val;
        public Dummy(int val)
        {
            Val = val;
        }
    }
    public class WhereOrFindAll
    {
        const int ElCount = 20000000;
        const int FilterVal =1000;
        const int MaxVal = 2000;
        const bool CheckSum = true; // Checks sum of elements in list of resutls
        static List list = new List();
        public delegate void FuncToTest();

        public static long TestTicks(FuncToTest function, string msg)
        {
            Stopwatch watch = new Stopwatch();
            watch.Start();
            function();
            watch.Stop();
            Console.Write("\r\n"+msg + "\t ticks: " + (watch.ElapsedTicks));
            return watch.ElapsedTicks;
        }
        static void Check(List list)
        {
            if (!CheckSum) return;
            Stopwatch watch = new Stopwatch();
            watch.Start();

            long res=0;
            int count = list.Count;
            for (int i = 0; i < count; i++)     res += list[i].Val;
            for (int i = 0; i < count; i++)     res -= (long)(list[i].Val * 0.3);

            watch.Stop();
            Console.Write("\r\n\nCheck sum: " + res.ToString() + "\t iteration ticks: " + watch.ElapsedTicks);
        }
        static void Check(IEnumerable ieNumerable)
        {
            if (!CheckSum) return;
            Stopwatch watch = new Stopwatch();
            watch.Start();

            IEnumerator ieNumerator = ieNumerable.GetEnumerator();
            long res = 0;
            while (ieNumerator.MoveNext())  res += ieNumerator.Current.Val;
            ieNumerator=ieNumerable.GetEnumerator();
            while (ieNumerator.MoveNext())  res -= (long)(ieNumerator.Current.Val * 0.3);

            watch.Stop();
            Console.Write("\r\n\nCheck sum: " + res.ToString() + "\t iteration ticks :" + watch.ElapsedTicks);
        }
        static void Generate()
        {
            if (list.Count > 0)
                return;
            var rand = new Random();
            for (int i = 0; i < ElCount; i++)
                list.Add(new Dummy(rand.Next(MaxVal)));

        }
        static void For()
        {
            List resList = new List();
            int count = list.Count;
            for (int i = 0; i < count; i++)
            {
                if (list[i].Val < FilterVal)
                    resList.Add(list[i]);
            }      
            Check(resList);
        }
        static void Foreach()
        {
            List resList = new List();
            int count = list.Count;
            foreach (Dummy dummy in list)
            {
                if (dummy.Val < FilterVal)
                    resList.Add(dummy);
            }
            Check(resList);
        }
        static void WhereToList()
        {
            List resList = list.Where(x => x.Val < FilterVal).ToList();
            Check(resList);
        }
        static void WhereIEnumerable()
        {
            Stopwatch watch = new Stopwatch();
            IEnumerable iEnumerable = list.Where(x => x.Val < FilterVal);
            Check(iEnumerable);
        }
        static void FindAll()
        {
            List resList = list.FindAll(x => x.Val < FilterVal);
            Check(resList);
        }
        public static void Run()
        {
            Generate();
            long[] ticks = { 0, 0, 0, 0, 0 };
            for (int i = 0; i < 10; i++)
            {
                ticks[0] += TestTicks(For, "For \t\t");
                ticks[1] += TestTicks(Foreach, "Foreach \t");
                ticks[2] += TestTicks(WhereToList, "Where to list \t");
                ticks[3] += TestTicks(WhereIEnumerable, "Where Ienum \t");
                ticks[4] += TestTicks(FindAll, "FindAll \t");
                Console.Write("\r\n---------------");
            }
            for (int i = 0; i < 5; i++)
                Console.Write("\r\n"+ticks[i].ToString());
        }
    
    }

    class Program
    {
        static void Main(string[] args)
        {
            WhereOrFindAll.Run();
            Console.Read();
        }
    }
}

Results(ticks) - CheckSum enabled(some operations on results), mode: release without debugging(CTRL+F5):

 - 16,222,276 (for ->list)
 - 17,151,121 (foreach -> list)
 -  4,741,494 (where ->list)
 - 27,122,285 (where ->ienum)
 - 18,821,571 (findall ->list)

CheckSum disabled (not using returned list at all):

 - 10,885,004 (for ->list)
 - 11,221,888 (foreach ->list)
 - 18,688,433 (where ->list)
 -      1,075 (where ->ienum)
 - 13,720,243 (findall ->list)

Your results can be slightly different, to get real results you need more iterations.