Generate multiple random numbers without repetition

Question

I’ve made some attempts to make a function that returns random numbers that don’t repeat themselves, I’ve made some attempts but none have succeeded, if you can show me a function that does that thank you.

Answer 1

First, generate an ordered list, in this example from 1 to 1000:

var maximo = 1000;

var i, arr = [];
for (i = 0; i < maximo; i++) {
   arr[i] = i + 1;
}

then shuffle the numbers within this array:

var p, n, tmp;
for (p = arr.length; p;) {
    n = Math.random() * p-- | 0;
    tmp = arr[n];
    arr[n] = arr[p];
    arr[p] = tmp;
}

Then just take the first items of the array, in order, from 1 until the amount of results you want, as they are already randomly shuffled, and no repeat.

See example with results on jsFiddle

_{adapted response of https://stackoverflow.com/questions/10694668/javascript-to-generate-50-no-repeat-random-numbers}

If you need a few figures:

This technique is efficient even with few values, in this case simply shorten the loop to "shuffle" only the required amount of numbers:

for (p = quantidade; p;) {

In this way, only the first values, indicated by the variable, will be "shuffled" quantidade.

About the algorithm

This algorithm is the Fisher-Yates, as reinforced the colleague @woliveirajr in the comments, and on another issue, the colleague @Fabridamazio found an interesting analysis comparing Fisher-Yates to Shuffling Brute Force.

It’s worth a read:

Analysis of a Brute-Force Shuffle

Answer 2

The solution that occurs to me is to create an array and add to it the values already created/drawn, and look in the array if the value already exists before exporting a new one.

This solution allows you to draw values one by one as well as draw them all at once.

var sorteados = [];
var valorMaximo = 1000;

function criarUnico() {
    if (sorteados.length == valorMaximo) {
        if (confirm('Já não há mais! Quer recomeçar?')) sorteados = [];
        else return;
    }
    var sugestao = Math.ceil(Math.random() * valorMaximo); // Escolher um numero ao acaso
    while (sorteados.indexOf(sugestao) >= 0) {  // Enquanto o numero já existir, escolher outro
        sugestao = Math.ceil(Math.random() * valorMaximo);
    }
    sorteados.push(sugestao); // adicionar este numero à array de numeros sorteados para futura referência
    return sugestao; // devolver o numero único
}

So, to draw a number just use:

criarUnico(); // que retorna um valor único

Example

Answer 3

I use this solution of mine for simplicity, since it uses the method Sort(), native to the language:

var x = new Array(1000);
for(var i=1; i<1001; i++) {
    x[i] = i; 
}

x.sort(function(a,b){ return (Math.round(Math.random())-0.5); });

However, the method used by @Bacco will always be faster, since it is not necessary to recreate the array.

Answer 4

function sorteado(max,quant) {
    var numeroS = []
    while (numeroS.length < quant) {
      e = Math.ceil(Math.random() * max);
      if (numeroS.indexOf(e) == -1) {
        numeroS.push(e)
      }
    }
   return numeroS
}
console.log(sorteado(1000,16))

Answer 5

Or you can run this way:

function getRandom(maxNum, qtdMax) {
  let n = 1;
  const lista = [];
  const val = () => Math.floor(Math.random() * maxNum + 1);
  
  do {
    while (n <= qtdMax) {
      let numero = val();

      if (lista.indexOf(numero) === -1) {
        lista.push(numero)
      } else {n -= 1};
      n += 1
    };
  } while (lista.length < qtdMax);

  lista.sort((a, b) => a - b);
  console.log(lista);
  return lista;
}

getRandom(60, 6);

In the above example, I left to run a 6-digit random combination (second function parameter) with value limit at 60 (first function parameter). So you can run the list only once for the amount of characters you want and the random number limit without making as many iterations. Detail, I put a Sort to organize the list upwards.

In a practical example, you can search for the data by index in the for loop, or unstructured:

const get = getRandom(60, 6);

for (const i in get) {
  const texto = `Index: ${i} = ${get[i]}`
  console.log(texto)
}

const [ num1 ] = get

console.log(num1)