LINQ Any VS Exists - What s the difference

Question

Using LINQ on collections  what is the difference between the following lines of code   if  coll Any i   gt  i Value     and  if  coll Exists i   gt  i Value     Update 1  When I disassemble  Exists it looks like there is no code   Update 2  Anyone know why there is no code there for this one

User · Answer

Additionally  this will only work if Value is of type bool  Normally this is used with predicates  Any predicate would be generally used find whether there is any element satisfying a given condition  Here you re just doing a map from your element i to a bool property  It will search for an  i  whose Value property is true  Once done  the method will return true

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See documentation  List Exists  Object method - MSDN      Determines whether the List T  contains elements that match the conditions defined by the specified predicate    This exists since  NET 2 0  so before LINQ  Meant to be used with the Predicate delegate  but lambda expressions are backward compatible  Also  just List has this  not even IList   IEnumerable Any  Extension method - MSDN         Determines whether any element of a sequence satisfies a condition    This is new in  NET 3 5 and uses Func TSource  bool  as argument  so this was intended to be used with lambda expressions and LINQ   In behaviour  these are identical

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When you correct the measurements - as mentioned above  Any and Exists  and adding average - we ll get following output    Executing search Exists   1000 times      Average Exists    35566 023 Fastest Exists   execution  32226   Executing search Any   1000 times      Average Any    58852 435 Fastest Any   execution  52269 ticks  Benchmark finished  Press any key

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TLDR  Performance-wise Any seems to be slower  if I have set this up properly to evaluate both values at almost same time           var list1   Generate 1000000           var forceListEval   list1 SingleOrDefault o   gt  o     0123456789012            if  forceListEval     sdsdf                         var s   string Empty              var start2   DateTime Now              if   list1 Exists o   gt  o     0123456789012                                  var end2   DateTime Now                  s      Exists      end2 Subtract start2                              var start1   DateTime Now              if   list1 Any o   gt  o     0123456789012                                  var end1   DateTime Now                  s     Any     end1 Subtract start1                              if   s Contains  sdfsd                                   testing list generator   private List lt string gt  Generate int count                var list   new List lt string gt             for  int i   0  i  lt  count  i                          list Add  new string              Enumerable Repeat  ABCDEFGHIJKLMNOPQRSTUVWXYZ   13                   Select s   gt                                        var cryptoResult   new byte 4                       new RNGCryptoServiceProvider   GetBytes cryptoResult                       return s new Random BitConverter ToInt32 cryptoResult  0   Next s Length                                        ToArray                          return list          With 10M records       Any  00 00 00 3770377 Exists  00 00 00 2490249    With 5M records       Any  00 00 00 0940094 Exists  00 00 00 1420142    With 1M records       Any  00 00 00 0180018 Exists  00 00 00 0090009    With 500k   I also flipped around order in which they get evaluated to see if there is no additional operation associated with whichever runs first         Exists  00 00 00 0050005 Any  00 00 00 0100010    With 100k records       Exists  00 00 00 0010001 Any  00 00 00 0020002    It would seem Any to be slower by magnitude of 2   Edit  For 5 and 10M records I changed the way it generates the list and Exists suddenly became slower than Any which implies there s something wrong in the way I am testing   New testing mechanism   private static IEnumerable lt string gt  Generate int count                var cripto   new RNGCryptoServiceProvider            Func lt string gt  getString        gt  new string              Enumerable Repeat  ABCDEFGHIJKLMNOPQRSTUVWXYZ   13                   Select s   gt                                        var cryptoResult   new byte 4                       cripto GetBytes cryptoResult                       return s new Random BitConverter ToInt32 cryptoResult  0   Next s Length                                        ToArray              var list   new ConcurrentBag lt string gt             var x   Parallel For 0  count  o   gt  list Add getString              return list             private static void Test                 var list   Generate 10000000           var list1   list ToList            var forceListEval   list1 SingleOrDefault o   gt  o     0123456789012            if  forceListEval     sdsdf                         var s   string Empty               var start1   DateTime Now              if   list1 Any o   gt  o     0123456789012                                  var end1   DateTime Now                  s      Any      end1 Subtract start1                              var start2   DateTime Now              if   list1 Exists o   gt  o     0123456789012                                  var end2   DateTime Now                  s      Exists      end2 Subtract start2                              if   s Contains  sdfsd                                             Edit2  Ok so to eliminate any influence from generating test data I wrote it all to file and now read it from there    private static void Test                 var list1   File ReadAllLines  test txt   Take 500000  ToList            var forceListEval   list1 SingleOrDefault o   gt  o     0123456789012            if  forceListEval     sdsdf                         var s   string Empty              var start1   DateTime Now              if   list1 Any o   gt  o     0123456789012                                  var end1   DateTime Now                  s      Any      end1 Subtract start1                              var start2   DateTime Now              if   list1 Exists o   gt  o     0123456789012                                  var end2   DateTime Now                  s      Exists      end2 Subtract start2                              if   s Contains  sdfsd                                                  10M        Any  00 00 00 1640164 Exists  00 00 00 0750075     5M       Any  00 00 00 0810081 Exists  00 00 00 0360036    1M       Any  00 00 00 0190019 Exists  00 00 00 0070007    500k       Any  00 00 00 0120012 Exists  00 00 00 0040004

User · Answer

The difference is that Any is an extension method for any IEnumerable lt T gt  defined on System Linq Enumerable   It can be used on any IEnumerable lt T gt  instance     Exists does not appear to be an extension method   My guess is that coll is of type List lt T gt    If so Exists is an instance method which functions very similar to Any     In short  the methods are essentially the same   One is more general than the other    Any also has an overload which takes no parameters and simply looks for any item in the enumerable   Exists has no such overload

User · Answer

As a continuation on Matas  answer on benchmarking   TL DR  Exists   and Any   are equally fast   First off  Benchmarking using Stopwatch is not precise  see series0ne s answer on a different  but similiar  topic   but it is far more precise than DateTime   The way to get really precise readings is by using Performance Profiling  But one way to get a sense of how the two methods  performance measure up to each other is by executing both methods loads of times and then comparing the fastest execution time of each  That way  it really doesn t matter that JITing and other noise gives us bad readings  and it does   because both executions are  equally misguiding  in a sense   static void Main string   args                Console WriteLine  Generating list               List lt string gt  list   GenerateTestList 1000000           var s   string Empty           Stopwatch sw          Stopwatch sw2          List lt long gt  existsTimes   new List lt long gt             List lt long gt  anyTimes   new List lt long gt              Console WriteLine  Executing               for  int j   0  j  lt  1000  j                          sw   Stopwatch StartNew                if   list Exists o   gt  o     0123456789012                                  sw Stop                    existsTimes Add sw ElapsedTicks                                    for  int j   0  j  lt  1000  j                          sw2   Stopwatch StartNew                if   list Exists o   gt  o     0123456789012                                  sw2 Stop                    anyTimes Add sw2 ElapsedTicks                                    long existsFastest   existsTimes Min            long anyFastest   anyTimes Min             Console WriteLine string Format  Fastest Exists   execution   0  ticks nFastest Any   execution   1  ticks   existsFastest ToString    anyFastest ToString              Console WriteLine  Benchmark finished  Press any key             Console ReadKey               public static List lt string gt  GenerateTestList int count                var list   new List lt string gt             for  int i   0  i  lt  count  i                          Random r   new Random                int it   r Next 0  100               list Add new string  s   it                      return list          After executing the above code 4 times  which in turn do 1 000 Exists   and Any   on a list with 1 000 000 elements   it s not hard to see that the methods are pretty much equally fast   Fastest Exists   execution  57881 ticks Fastest Any   execution  58272 ticks  Fastest Exists   execution  58133 ticks Fastest Any   execution  58063 ticks  Fastest Exists   execution  58482 ticks Fastest Any   execution  58982 ticks  Fastest Exists   execution  57121 ticks Fastest Any   execution  57317 ticks   There is a slight difference  but it s too small a difference to not be explained by background noise  My guess would be that if one would do 10 000 or 100 000 Exists   and Any   instead  that slight difference would disappear more or less

[c#] LINQ .Any VS .Exists - What's the difference?

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