Create an array with random values

Question

How can I create an array with 40 elements  with random values from 0 to 39   Like   4  23  7  39  19  0  9  14         I tried using solutions from here   http   freewebdesigntutorials com javaScriptTutorials jsArrayObject randomizeArrayElements htm  but the array I get is very little randomized  It generates a lot of blocks of successive numbers

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Here s a solution that shuffles a list of unique numbers  no repeats  ever    for  var a    i 0 i lt 40   i  a i  i      http   stackoverflow com questions 962802 962890 function shuffle array      var tmp  current  top   array length    if top  while --top        current   Math floor Math random      top   1        tmp   array current       array current    array top       array top    tmp        return array     a   shuffle a     If you want to allow repeated values  which is not what the OP wanted  then look elsewhere

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Even shorter ES6 approach   Array 40  fill   map      gt  Math round Math random     40     Also  you could have a function with arguments   const randomArray    length  max    gt     Array length  fill   map      gt  Math round Math random     max

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Shortest  -       Array 40   map e  gt    Math random   40

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Generators An array of length 40 of 40 random possible values  0 - 39  without repeating values is better to shuffle it as  Phrogz and  Jared Beck explain  Another approach  just for the records  could be using generators  But this approach lacks of performance compared to other proposed solutions  function  generateRandomIterable n  range      for  let i   0  i  lt  n  i          yield    Math random     range         const randomArr       generateRandomIterable 40 40

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Quirk single-line solutions on every day   Values in arrays is total random  so when you will be use this snippets  it will different   An array  length 10  with random chars in lowercase  Array apply null  Array 10   map function     return String fromCharCode Math floor Math random      123 - 97    97               k    a    x    y    n    w    m    q    b    j      An array  length 10  with random integer numbers from 0 to 99  Array apply null  Array 10   map function     return Math floor Math random     100   100             86  77  83  27  79  96  67  75  52  21     An array random dates  from 10 years to ago to now   Array apply null  Array 10   map function     return new Date  new Date    getFullYear   - Math floor Math random     10   Math floor Math random     12   Math floor Math random     29             2008-08-22T21 00 00 000Z    2007-07-17T21 00 00 000Z    2015-05-05T21 00 00 000Z    2011-06-14T21 00 00 000Z    2009-07-23T21 00 00 000Z    2009-11-13T22 00 00 000Z    2010-05-09T21 00 00 000Z    2008-01-05T22 00 00 000Z    2016-05-06T21 00 00 000Z    2014-08-06T21 00 00 000Z     An array  length 10  random strings  Array apply null  Array 10   map function     return Array apply null  Array Math floor Math random     10    3    map function     return String fromCharCode Math floor Math random      123 - 97    97       join                 cubjjhaph            bmwy            alhobd            ceud            tnyullyn            vpkdflarhnf            hvg            arazuln            jzz            cyx      Other useful things you may found here https   github com setivolkylany nodejs-utils blob master utils faker js

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The shortest approach  ES6       randomly generated N   40 length array 0  lt   A N   lt   39 Array from  length  40        gt  Math floor Math random     40         Enjoy

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I am pretty sure that this is the shortest way to create your random array without any repeats  var random array   new Array 40  fill   map  a  i    gt  a   i  sort      gt  Math random   - 0 5

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Using some new ES6 features  this can now be achieved using   function getRandomInt min  max         use strict       if  max  lt  min               Swap min and max          min  max     min  max                 Generate random number n  where min  lt   n  lt   max     let range   max - min   1      return Math floor Math random     range    min     let values   Array from  length  40        gt  getRandomInt 0  40     console log values     Note that this solution will only work in modern browsers that support these ES6 features  arrow functions and Array from

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Since the range of numbers is constrained  I d say the best thing to do is generate the array  fill it with numbers zero through 39  in order   then shuffle it

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If you need it with random unique values from 0   length range   const randomRange   length   gt      const results        const possibleValues   Array from   length     value  i    gt  i     for  let i   0  i  lt  length  i    1        const possibleValuesRange   length -  length - possibleValues length      const randomNumber   Math floor Math random     possibleValuesRange      const normalizedRandomNumber   randomNumber     possibleValuesRange   randomNumber   possibleValuesRange      const  nextNumber    possibleValues splice normalizedRandomNumber  1       results push nextNumber         return results    randomRange 5      3  0  1  4  2

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Because   has higher precedence than    it can be shorter by using  0 to replace Math floor        Array 40   map e  gt Math random   40 0

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ES5   function randomArray length  max        return Array apply null  Array length   map function             return Math round Math random     max               ES6   randomArray    length  max    gt      new Array length        map      gt  Math round Math random     max

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A little late to the party  but I use randojs com for randomness because it makes stuff like this super easy  You can get a randomly shuffled array of numbers from 0 through 39 just like this   x000D   x000D  console log randoSequence 40    x000D   lt script src  https   randojs com 1 0 0 js  gt  lt  script gt  x000D   x000D   x000D   No fuss with the logistics of it all- plus it s super readable and easy to understand

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the array I get is very little randomized  It generates a lot of blocks of successive numbers      Sequences of random items often contain blocks of successive numbers  see the Gambler s Fallacy   For example         we have just tossed four heads in a row    Since the probability of   a run of five successive heads is only 1 32    a person subject to the   gambler s fallacy might believe that this next flip was less likely to   be heads than to be tails    http   en wikipedia org wiki Gamblers fallacy

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Here is a ES6 function that allows a min and a max and will generate an array of unique values in random order that contain all the number from min to max inclusive  const createRandomNumbers    min  max    gt      const randomNumbers   new Set     const range   max - min   1    while  randomNumbers size  lt  range        randomNumbers add    Math random     range          return     randomNumbers

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from the page suggested by  Phrogz  for  var i 0 nums    i lt 49 i    nums i    n i  rand Math random      nums sort  function a b   a a rand  b b rand  return a lt b -1 a gt b 1 0

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function shuffle maxElements          create ordered array   0 1 2 3  maxElements     for  var temArr       i   0  i  lt  maxElements  i              temArr i    i             for  var finalArr    maxElements   i   0  i  lt  maxElements  i                remove rundom element form the temArr and push it into finalArrr         finalArr i    temArr splice Math floor Math random      maxElements - i    1  0              return finalArr     I guess this method will solve the issue with the probabilities  only limited by random numbers generator

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Refer below  -  let arr   Array apply null   length  1000   map Function call  Math random     will create array with 1000 elements

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I needed something a bit different than what these solutions gave  in that I needed to create an array with a number of distinct random numbers held to a specified range  Below is my solution    function getDistinctRandomIntForArray array  range      var n   Math floor  Math random     range       if array indexOf n     -1               return n        else       return getDistinctRandomIntForArray array  range            function generateArrayOfRandomInts count  range       var array           for  i 0  i lt count    i       array i    getDistinctRandomIntForArray array  range            return array       I would have preferred to not create a loop that has the possibility to end up with a lot of unnecessary calls  if your count  and range are high and are close to the same number  but this is the best I could come up with

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Math random   will return a number between 0 and 1 exclusive   So  if you want 0-40  you can multiple it by 40  the highest the result can ever be is what you re multiplying by   var arr       for  var i 0  t 40  i lt t  i          arr push Math round Math random     t     document write arr     http   jsfiddle net robert tUW89

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var myArray       var arrayMax   40  var limit   arrayMax   1  for  var i   0  i  lt  arrayMax  i        myArray push Math floor Math random   limit        This above is the traditional way of doing it but I second  Pointy and  Phrogz if you want to avoid duplicates in your array without having to do expensive computation

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let randomNumber   Array from  length  6        gt  Math floor Math random     39      limited the array to 6 values to make it easy to see

[javascript] Create an array with random values

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