Generating random unique values C

Question

I ve searched for a while and been struggling to find this  I m trying to generate several random  unique numbers is C   I m using System Random  and I m using a DateTime Now Ticks seed   public Random a   new Random DateTime Now Ticks GetHashCode     private void NewNumber         MyNumber   a Next 0  10       I m calling NewNumber   regularly  but the problem is I often get repeated numbers  Some people suggested because I was declaring the random every time I did it  it would not produce a random number  so I put the declaration outside my function  Any suggestions or better ways than using System Random   Thank you

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You can use basic Random Functions of C   Random ran   new Random    int randomno   ran Next 0 100     you can now use the value in the randomno in anything you want but keep in mind that this will generate a random number between 0 and 100 Only and you can extend that to any figure

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Try this   private void NewNumber            Random a   new Random Guid newGuid   GetHashCode          MyNumber   a Next 0  10         Some Explnations    Guid   base on here   Represents a globally unique identifier  GUID   Guid newGuid   produces a unique identifier like  936DA01F-9ABD-4d9d-80C7-02AF85C822A8    and it will be unique in all over the universe base on here   Hash code here produce a unique integer from our unique identifier  so Guid newGuid   GetHashCode    gives us a unique number and the random class will produce real random numbers throw this   Sample  https   rextester com ODOXS63244  generated ten random numbers with this approach with result of   -1541116401 7 -1936409663 3 -804754459 8 1403945863 3 1287118327 1 2112146189 1 1461188435 9 -752742620 4 -175247185 4 1666734552 7   we got two 1s next to each other  but the hash codes do not same

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And here my version of finding N random unique numbers using HashSet  Looks pretty simple  since HashSet can contain only different items  It s interesting - would it be faster then using List or Shuffler   using System  using System Collections Generic   namespace ConsoleApplication1       class RnDHash               static void Main                         HashSet lt int gt  rndIndexes   new HashSet lt int gt                 Random rng   new Random                int maxNumber              Console Write  Please input Max number                  maxNumber   int Parse Console ReadLine                 int iter   0              while  rndIndexes Count    maxNumber                                int index   rng Next maxNumber                   rndIndexes Add index                   iter                              Console WriteLine  Random numbers were found in  0  iterations     iter               foreach  int num in rndIndexes                                Console WriteLine num                             Console ReadKey

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I m posting a correct implementation of a shuffle algorithm  since the other one posted here doesn t produce a uniform shuffle   As the other answer states  for small numbers of values to be randomized  you can simply fill an array with those values  shuffle the array  and then use however many of the values that you want   The following is an implementation of the Fisher-Yates Shuffle  aka the Knuth Shuffle    Read the  implementation errors  section of that link  search for  always selecting j from the entire range of valid array indices on every iteration   to see some discussion about what is wrong with the other implementation posted here    using System  using System Collections Generic   namespace ConsoleApplication2       static class Program               static void Main string   args                        Shuffler shuffler   new Shuffler                List lt int gt  list   new List lt int gt   1  2  3  4  5  6  7  8  9                shuffler Shuffle list                foreach  int value in list                                Console WriteLine value                                           lt summary gt Used to shuffle collections  lt  summary gt       public class Shuffler                    lt summary gt Creates the shuffler with a  lt see cref  MersenneTwister   gt  as the random number generator  lt  summary gt           public Shuffler                          rng   new Random                            lt summary gt Shuffles the specified array  lt  summary gt               lt typeparam name  T  gt The type of the array elements  lt  typeparam gt               lt param name  array  gt The array to shuffle  lt  param gt           public void Shuffle lt T gt  IList lt T gt  array                        for  int n   array Count  n  gt  1                                  int k    rng Next n                   --n                  T temp   array n                   array n    array k                   array k    temp                                   private System Random  rng

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hi here i posted one video  and it explains how to generate unique random number     public List lt int gt  random generator       Random random   new Random        List lt int gt  random container   new List lt int gt         do          int random number   random next 10          if  random container contains random number           random container add random number           while random container count  10          return random container         here     in random container you will get non repeated 10 numbers starts from 0  to 9 10 numbers  as random   thank you

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You could also use a dataTable storing each random value  then simply perform the random method while    values in the dataColumn

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Same as  Habib s answer  but as a function  List lt int gt  randomList   new List lt int gt     int UniqueRandomInt int min  int max        var rand   new Random        int myNumber      do              myNumber   rand Next min  max         while  randomList Contains myNumber        return myNumber     If randomList is a class property  UniqueRandomInt will return unique integers in the context of the same instance of that class  If you want it to be unique globally  you will need to make randomList static

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This console app will let you shuffle the alphabet five times with different orders   using System  using System Linq   namespace Shuffle       class Program               static Random rnd   new Random            static void Main string   args                        var alphabet   new string      a    b    c    d    e    f    g    h    i    j    k    l    m    n    o    p    q    r    s    t    u    v    w    x    y    z                 Console WriteLine  Alphabet    0    string Join      alphabet                 for  int i   0  i  lt  5  i                                  var shuffledAlphabet   GetShuffledAlphabet alphabet                   Console WriteLine  SHUFFLE  0    1    i  string Join      shuffledAlphabet                                     static string   GetShuffledAlphabet string   arr                        int    uniqueNumbers   new int  arr Length               string   shuffledAlphabet   new string arr Length                for  int i   0  i  lt  arr Length  i                                  int uniqueNumber   GenerateUniqueNumber uniqueNumberArrays                   uniqueNumberArrays i    uniqueNumber                  newArray i    arr uniqueNumber                              return shuffledAlphabet                     static int GenerateUniqueNumber int    uniqueNumbers                        int number   rnd Next uniqueNumbers Length                if   uniqueNumbers Any r   gt  r    number                                 return number                             return GenerateUniqueNumber uniqueNumbers

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Depending on what you are really after you can do something like this   using System  using System Collections Generic  using System Linq   namespace SO14473321       class Program               static void Main                         UniqueRandom u   new UniqueRandom Enumerable Range 1 10                for  int i   0  i  lt  10  i                                  Console Write   0    u Next                                        class UniqueRandom               private readonly List lt int gt   currentList          private readonly Random  random   new Random             public UniqueRandom IEnumerable lt int gt  seed                         currentList   new List lt int gt  seed                      public int Next                         if   currentList Count    0                                throw new ApplicationException  No more numbers                               int i    random Next  currentList Count               int result    currentList i                currentList RemoveAt i               return result

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I m calling NewNumber   regularly  but the problem is I often get repeated numbers   Random Next doesn t guarantee the number to be unique  Also your range is from 0 to 10 and chances are you will get duplicate values  May be you can setup a list of int and insert random numbers in the list after checking if it doesn t contain the duplicate  Something like  public Random a   new Random       replace from new Random DateTime Now Ticks GetHashCode                                        Since similar code is done in default constructor internally public List lt int gt  randomList   new List lt int gt     int MyNumber   0  private void NewNumber         MyNumber   a Next 0  10       if   randomList Contains MyNumber           randomList Add MyNumber

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NOTE  I dont recommend this     Here s a  oneliner  as well     This code generates numbers between 1 - 100 and then takes 10 of them  var result   Enumerable Range 1 101  OrderBy g   gt  Guid NewGuid    Take 10  ToArray

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I noted that the accepted answer keeps adding int to the list and keeps checking them with if   randomList Contains MyNumber   and I think this doesn t scale well  especially if you keep asking for new numbers   I would do the opposite    Generate the list at startup  linearly Get a random index from the list Remove the found int from the list   This would require a slightly bit more time at startup  but will scale much much better   public class RandomIntGenerator       public Random a   new Random        private List lt int gt   validNumbers       private RandomIntGenerator int desiredAmount  int start   0                 validNumbers   new List lt int gt             for  int i   0  i  lt  desiredAmount  i                 validNumbers Add i   start              private int GetRandomInt                 if   validNumbers Count    0                          you could throw an exception here             return -1                    else                       var nextIndex   a Next 0   validNumbers Count - 1               var number       validNumbers nextIndex                validNumbers RemoveAt nextIndex               return number

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This is a unity only answer   Check this ready-to-use method  Give in a range  amp  count of number you want to get   public static int   getUniqueRandomArray int min  int max  int count        int   result   new int count       List lt int gt  numbersInOrder   new List lt int gt         for  var x   min  x  lt  max  x              numbersInOrder Add x             for  var x   0  x  lt  count  x              var randomIndex   UnityEngine Random Range 0  numbersInOrder Count           result x    numbersInOrder randomIndex           numbersInOrder RemoveAt randomIndex              return result

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randomNumber function return unqiue integer value between 0 to 100000     bool check     new bool 100001     Random r   new Random      public int randomNumber           int num   r Next 0 100000          while check num     true                 num   r Next 0 100000              check num    true     return num

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unique random number from 0 to 9       int sum   0          int   hue   new int 10           for  int i   0  i  lt  10  i                           int m              do                               m   rand Next 0  10                 while  hue Contains m   amp  amp  sum    45               if   hue Contains m                                 hue i    m                  sum   sum   m

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It s may be a little bit late  but here is more suitable code  for example when you need to use loops               List lt int gt  genered   new List lt int gt                  Random rnd   new Random                 for int x   0  x  lt  files Length  x                                  int value   rnd Next 0  files Length - 1                   while  genered Contains value                                         value   rnd Next 0  files Length - 1                                     genered Add value                    returnFiles x    files value

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You might try shuffling an array of possible ints if your range is only 0 through 9  This adds the benefit of avoiding any conflicts in the number generation   var nums   Enumerable Range 0  10  ToArray    var rnd   new Random        Shuffle the array for  int i   0 i  lt  nums Length   i        int randomIndex   rnd Next nums Length       int temp   nums randomIndex       nums randomIndex    nums i       nums i    temp        Now your array is randomized and you can simply print them in order for  int i   0 i  lt  nums Length   i      Console WriteLine nums i

[c#] Generating random, unique values C#

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