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Performance comparison of using a List as opposed to an Array

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17 Jun 2010CPOL 52.5K   3   47
Benchmark both List and string[].

Introduction

The objective of this article is to elucidate you, fellow developers, to really evaluate the need of using a generic List<T> instead of an old string[], since usually the cost is overlooked.

Using the Code

I've built a simple example to compare the performance for reading and writing to a List<string> and a string[]. Concerning the writing time in milliseconds, for 100000 randomly generated items, the string[] outperformed the List<string> by approximately 8ms.

C#
//Write
const int size = 100000;
Stopwatch startList = new Stopwatch();
startList.Start();
List<string> listString = new List<string>(size);
for (int i = 0; i <= size; i++)
{
    string toAdd = Guid.NewGuid().ToString();
    listString.Add(toAdd);
}
startList.Stop();
TimeSpan durationList = startList.Elapsed;

Stopwatch startArray = new Stopwatch();
startArray.Start();
string[] arrayString = new string[size];
for (int i = 0; i < size; i++)
{
    string toAdd = Guid.NewGuid().ToString();
    arrayString[i] = toAdd;
}
startArray.Stop();
TimeSpan durationArray= startArray.Elapsed;

When reading, the string[] outperforms the List<string> by approximately 2.5 times faster!!

C#
//Read
Stopwatch startListRead = new Stopwatch();
startListRead.Start();
for (int i = 0; i <= listString.Count - 1; i++)
{
    string str = listString[i];
}
startListRead.Stop();
TimeSpan durationListRead = startListRead.Elapsed;

Stopwatch startArrayRead = new Stopwatch();
startArrayRead.Start();
for (int i = 0; i <= arrayString.Length - 1; i++)
{
    string str = arrayString[i];
}
startArrayRead.Stop();
TimeSpan durationArrayRead = startArrayRead.Elapsed;

And you can still do this with LINQ to Objects with an array, as you do with your List<string>:

C#
//Perform our LINQ query on an Array just like a List<T>
var result = from i in arrayString
         where i.StartsWith("a")
         select i;

Results:

benchmarkres.png

So, bottom line, you should consider if you really need the List<T> as opposed to an array because there are serious performance costs that will affect your application.

Points of Interest

Creating concerns on performance of instructions being used in your applications.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
Software Developer (Senior) Truphone
Portugal Portugal
This member has not yet provided a Biography. Assume it's interesting and varied, and probably something to do with programming.

Comments and Discussions

 
GeneralRe: Not the timings I get Pin
supernova566615-Jun-10 3:09
supernova566615-Jun-10 3:09 
GeneralRe: Not the timings I get Pin
Magnus_15-Jun-10 3:32
Magnus_15-Jun-10 3:32 
GeneralRe: Not the timings I get Pin
ricmrodrigues15-Jun-10 3:40
ricmrodrigues15-Jun-10 3:40 
GeneralRe: Not the timings I get Pin
ricmrodrigues15-Jun-10 3:52
ricmrodrigues15-Jun-10 3:52 
GeneralRe: Not the timings I get Pin
Dominic Pettifer15-Jun-10 7:04
Dominic Pettifer15-Jun-10 7:04 
GeneralRe: Not the timings I get Pin
ricmrodrigues15-Jun-10 22:27
ricmrodrigues15-Jun-10 22:27 
GeneralRe: Not the timings I get Pin
ricmrodrigues17-Jun-10 3:33
ricmrodrigues17-Jun-10 3:33 
GeneralTypo in code Pin
Dominic Pettifer17-Jun-10 3:42
Dominic Pettifer17-Jun-10 3:42 
Typo: You're initialising your List<string> to 100'000 (one hundred thousand) items but end up inserting 1'000'000 (one million) items into it, so again not a fair comparison. Please use a static const instead to store the number of items you are going to test, and refer to that variable in code (remember the DRY principle, helps prevent typos). Eg:

private const int ITERATIONS = 1000000;

for(int i = 0; i < ITERATIONS; i++)

Dominic Pettifer

Blog: www.dominicpettifer.co.uk

GeneralRe: Typo in code Pin
ricmrodrigues17-Jun-10 4:09
ricmrodrigues17-Jun-10 4:09 
GeneralStopWatch Pin
giammin15-Jun-10 3:02
giammin15-Jun-10 3:02 
GeneralRe: StopWatch Pin
ricmrodrigues15-Jun-10 3:39
ricmrodrigues15-Jun-10 3:39 
GeneralRe: StopWatch Pin
ricmrodrigues17-Jun-10 3:34
ricmrodrigues17-Jun-10 3:34 

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