Is a LINQ statement faster than a foreach loop

Question

I am writing a Mesh Rendering manager and thought it would be a good idea to group all of the meshes which use the same shader and then render these while I m in that shader pass     I am currently using a foreach loop  but wondered if utilising LINQ might give me a performance increase

User · Answer

This is actually quite a complex question. Linq makes certain things very easy to do, that if you implement them yourself, you might stumble over (e.g. linq .Except()). This particularly applies to PLinq, and especially to parallel aggregation as implemented by PLinq.

In general, for identical code, linq will be slower, because of the overhead of delegate invocation.

If, however, you are processing a large array of data, and applying relatively simple calculations to the elements, you will get a huge performance increase if:

You use an array to store the data.
You use a for loop to access each element (as opposed to foreach or linq).
- Note: When benchmarking, please everyone remember - if you use the same array/list for two consecutive tests, the CPU cache will make the second one faster. *

User · Answer

LINQ-to-Objects generally is going to add some marginal overheads  multiple iterators  etc   It still has to do the loops  and has delegate invokes  and will generally have to do some extra dereferencing to get at captured variables etc  In most code this will be virtually undetectable  and more than afforded by the simpler to understand code   With other LINQ providers like LINQ-to-SQL  then since the query can filter at the server it should be much better than a flat foreach  but most likely you wouldn t have done a blanket  select   from foo  anyway  so that isn t necessarily a fair comparison   Re PLINQ  parallelism may reduce the elapsed time  but the total CPU time will usually increase a little due to the overheads of thread management etc

User · Answer

I was interested in this question  so I did a test just now  Using  NET Framework 4 5 2 on an Intel R  Core TM  i3-2328M CPU   2 20GHz  2200 Mhz  2 Core s  with 8GB ram running Microsoft Windows 7 Ultimate   It looks like LINQ might be faster than for each loop  Here are the results I got   Exists   True Time     174 Exists   True Time     149   It would be interesting if some of you could copy  amp  paste this code in a console app and test as well  Before testing with an object  Employee  I tried the same test with integers  LINQ was faster there as well   public class Program       public class Employee               public int id          public string name          public string lastname          public DateTime dateOfBirth           public Employee int id string name string lastname DateTime dateOfBirth                        this id   id              this name   name              this lastname   lastname              this dateOfBirth   dateOfBirth                        public static void Main     gt  StartObjTest          region object test      public static void StartObjTest                 List lt Employee gt  items   new List lt Employee gt              for  int i   0  i  lt  10000000  i                          items Add new Employee i  name    i  lastname    i DateTime Today                       Test3 items  items Count-100           Test4 items  items Count - 100            Console Read                public static void Test3 List lt Employee gt  items  int idToCheck                 Stopwatch s   new Stopwatch            s Start             bool exists   false          foreach  var item in items                        if  item id    idToCheck                                exists   true                  break                                   Console WriteLine  Exists     exists           Console WriteLine  Time     s ElapsedMilliseconds               public static void Test4 List lt Employee gt  items  int idToCheck                 Stopwatch s   new Stopwatch            s Start             bool exists   items Exists e   gt  e id    idToCheck            Console WriteLine  Exists     exists           Console WriteLine  Time     s ElapsedMilliseconds                endregion        region int test     public static void StartIntTest                 List lt int gt  items   new List lt int gt              for  int i   0  i  lt  10000000  i                          items Add i                      Test1 items  -100           Test2 items  -100            Console Read               public static void Test1 List lt int gt  items int itemToCheck                 Stopwatch s   new Stopwatch            s Start             bool exists   false          foreach  var item in items                        if  item    itemToCheck                                exists   true                  break                                   Console WriteLine  Exists     exists           Console WriteLine  Time     s ElapsedMilliseconds               public static void Test2 List lt int gt  items  int itemToCheck                 Stopwatch s   new Stopwatch            s Start             bool exists   items Contains itemToCheck            Console WriteLine  Exists     exists           Console WriteLine  Time     s ElapsedMilliseconds                endregion

User · Answer

Why should LINQ be faster  It also uses loops internally    Most of the times  LINQ will be a bit slower because it introduces overhead  Do not use LINQ if you care much about performance  Use LINQ because you want shorter better readable and maintainable code

User · Answer

It should probably be noted that the for loop is faster than the foreach  So for the original post  if you are worried about performance on a critical component like a renderer  use a for loop   Reference  In  NET  which loop runs faster    39 for  39  or   39 foreach  39

User · Answer

LINQ is slower now  but it might get faster at some point  The good thing about LINQ is that you don t have to care about how it works  If a new method is thought up that s incredibly fast  the people at Microsoft can implement it without even telling you and your code would be a lot faster   More importantly though  LINQ is just much easier to read  That should be enough reason

User · Answer

You might get a performance boost if you use parallel LINQ for multi cores  See Parallel LINQ  PLINQ   MSDN

[c#] Is a LINQ statement faster than a 'foreach' loop?

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