Generating unique random numbers integers between 0 and x

Question

I need to generate a set of unique  no duplicate  integers  and between 0 and a given number   That is   var limit   10  var amount   3    How can I use Javascript to generate 3 unique numbers between 1 and 10

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for i   0 i  lt amount  i          var randomnumber Math floor Math random   limit  1     document write randomnumber

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function generateRange pCount  pMin  pMax        min   pMin  lt  pMax   pMin   pMax      max   pMax  gt  pMin   pMax   pMin      var resultArr       randNumber      while   pCount  gt  0            randNumber   Math round min   Math random      max - min            if  resultArr indexOf randNumber     -1                resultArr push randNumber               pCount--                      return resultArr      Depending on range needed the method of returning the integer can be changed to  ceil  a b   round  a b   floor  a b   for  a b  is matter of adding 1 to min with floor

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Generates an array with numbers between    min and max randomly positioned      function genArr min  max  numOfSwaps     var size    max-min    1    numOfSwaps   numOfSwaps    size    var arr   Array apply null  Array size       for var i   0  j   min  i  lt  size  amp  j  lt   max  i    j          arr i    j         for var i   0  i  lt  numOfSwaps  i          var idx1   Math round Math random      size - 1        var idx2   Math round Math random      size - 1         var temp   arr idx1       arr idx1    arr idx2       arr idx2    temp         return arr        generating the array and using it to get 3 uniques numbers    var arr   genArr 1  10   for var i   0  i  lt  3  i        console log arr pop

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const getRandomNo    min  max    gt       min   Math ceil min      max   Math floor max      return Math floor Math random      max - min   1     min       This function returns a random integer between the specified values  The value is no lower than min  or the next integer greater than min if min isn t an integer  and is less than  but not equal to  max  Example  console log  Random no between 0 and 10   getRandomNo 0 10

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Math floor Math random      limit 1     Math random   generates a floating point number between 0 and 1  Math floor   rounds it down to an integer   By multiplying it by a number  you effectively make the range 0  number-1  If you wish to generate it in range from num1 to num2  do   Math floor Math random      num2-num1   1    num1    To generate more numbers  just use a for loop and put results into an array or write them into the document directly

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Just as another possible solution based on ES6 Set   arr  that can contain unique values only     Examples of usage       Get 4 unique rnd  numbers  from 0 until 4  inclusive   getUniqueNumbersInRange 4  0  5    - gt   5  0  4  1       Get 2 unique rnd  numbers  from -1 until 2  inclusive   getUniqueNumbersInRange 2  -1  2    - gt   1  -1       Get 0 unique rnd  numbers  empty result   from -1 until 2  inclusive   getUniqueNumbersInRange 0  -1  2    - gt          Get 7 unique rnd  numbers  from 1 until 7  inclusive   getUniqueNumbersInRange 7  1  7    - gt    3  1  6  2  7  5  4     The implementation   function getUniqueNumbersInRange uniqueNumbersCount  fromInclusive  untilInclusive            0 3  Check inputs      if  0  gt  uniqueNumbersCount  throw new Error  The number of unique numbers cannot be negative         if  fromInclusive  gt  untilInclusive  throw new Error   From  bound      fromInclusive              cannot be greater than  until  bound      untilInclusive              const rangeLength   untilInclusive - fromInclusive   1      if  uniqueNumbersCount  gt  rangeLength  throw new Error  The length of the range is     rangeLength                  fromInclusive           untilInclusive      that is smaller than             uniqueNumbersCount      specified count of result numbers          if  uniqueNumbersCount     0  return              1 3  Create a new  Set      object that stores unique values of any type  whether primitive values or object references         MDN - https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Set        Support  Google Chrome 38  2014 10   Firefox 13   IE 11      const uniqueDigits   new Set             2 3  Fill with random numbers              while  uniqueNumbersCount  gt  uniqueDigits size               Generate and add an random integer in specified range          const nextRngNmb   Math floor Math random     rangeLength    fromInclusive          uniqueDigits add nextRngNmb                  3 3  Convert  Set  with unique numbers into an array with  Array from            MDN     https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Array from        Support  Google Chrome 45   2015 09    Firefox 32   not IE     const resArray   Array from uniqueDigits       return resArray       The benefits of the current implementation    Have a basic check of input arguments     you will not get an unexpected output when the range is too small  etc   Support the negative range  not only from 0   e  g  randoms from -1000 to 500  etc  Expected behavior  the current most popular answer will extend the range  upper bound  on its own if input bounds are too small  An example  get 10000 unique numbers with a specified range from 0 until 10 need to throw an error due to too small range  10-0 1 11 possible unique numbers only   But the current top answer will hiddenly extend the range until 10000

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Here s a simple  one-line solution   var limit   10  var amount   3   randoSequence 1  limit  slice 0  amount     It uses randojs com to generate a randomly shuffled array of integers from 1 through 10 and then cuts off everything after the third integer  If you want to use this answer  toss this within the head tag of your HTML document    lt script src  https   randojs com 1 0 0 js  gt  lt  script gt

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var randomNums   function amount  limit    var result           memo        while result length  lt  amount        var num   Math floor  Math random     limit    1       if  memo num     memo num    num  result push num        return result      This seems to work  and its constant lookup for duplicates

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These answers either don t give unique values  or are so long  one even adding an external library to do such a simple task       1  generate a random number    2  if we have this random already then goto 1  else keep it    3  if we don t have desired quantity of randoms  then goto 1       x000D   x000D  function uniqueRandoms qty  min  max   x000D    var rnd  arr     x000D    do   do   rnd Math floor Math random   max  min   x000D        while arr includes rnd   x000D        arr push rnd   x000D      while arr length lt qty  x000D    return arr  x000D    x000D   x000D    generate 5 unique numbers between 1 and 10 x000D  console log  uniqueRandoms 5  1  10     x000D   x000D   x000D       and a compressed version of the same function   function uniqueRandoms qty min max  var a    do do r Math floor Math random   max  min while a includes r   a push r  while a length lt qty  return a

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Use the basic Math methods    Math random   returns a random number between 0 and 1  including 0  excluding 1   Multiply this number by the highest desired number  e g  10  Round this number downward to its nearest integer  Math floor Math random   10    1    Example     Example  including customisable intervals  lower bound  upper bound  var limit   10      amount   3      lower bound   1      upper bound   10      unique random numbers        if  amount  gt  limit  limit   amount    Infinite loop if you want more unique                                       Natural numbers than exist in a                                        given range while  unique random numbers length  lt  limit        var random number   Math floor Math random    upper bound - lower bound    lower bound       if  unique random numbers indexOf random number     -1                Yay  new random number         unique random numbers push  random number               unique random numbers is an array containing 3 unique numbers in the given range

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Here   s another algorithm for ensuring the numbers are unique    generate an array of all the numbers from 0 to x shuffle the array so the elements are in random order pick the first n   Compared to the method of generating random numbers until you get a unique one  this method uses more memory  but it has a more stable running time     the results are guaranteed to be found in finite time  This method works better if the upper limit is relatively low or if the amount to take is relatively high   My answer uses the Lodash library for simplicity  but you could also implement the algorithm described above without that library      assuming   is the Lodash library     generates  amount  numbers from 0 to  upperLimit  inclusive function uniqueRandomInts upperLimit  amount        var possibleNumbers     range upperLimit   1       var shuffled     shuffle possibleNumbers       return shuffled slice 0  amount

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I think  this is the most human approach  with using break from while loop   I explained it s mechanism in comments   function generateRandomUniqueNumbersArray  limit           we need to store these numbers somewhere     const array   new Array          how many times we added a valid number  for if statement later      let counter   0         we will be generating random numbers until we are satisfied     while  true               create that number         const newRandomNumber   Math floor Math random     limit              if we do not have this number in our array  we will add it         if   array includes newRandomNumber                 array push newRandomNumber               counter                         if we have enought of numbers  we do not need to generate them anymore         if  counter  gt   limit                break                         now hand over this stuff     return array      You can of course add different limit  your amount  to the last  if  statement  if you need less numbers  but be sure  that it is less or equal to the limit of numbers itself - otherwise it will be infinite loop

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Math floor Math random   limit  1

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Something like this  var limit   10  var amount   3  var nums   new Array     for int i   0  i  lt  amount  i          var add   true      var n   Math round Math random   limit   1      for int j   0  j  lt  limit length  j                  if nums j     n                        add   false                      if add                nums push n            else               i--

[javascript] Generating unique random numbers (integers) between 0 and 'x'

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