How to replace duplicates from array

Question

What is the way to remove duplicates from an array that generates random numbers? I've made random number generator that allows the user to type min/max values and how many numbers to generate. I also removed duplicates but if the user types 5 numbers to generate and there is 1 duplicate it will generate 4 numbers. How to add another number to replace the duplicate?

<html>

<head>
</head>

<body>
  <div id="container">
    <label for="fname">Min:</label>
    <input type="text" id="Min"><br><br>
    <label for="lname">Max:</label>
    <input type="text" id="Max"><br><br>
    <label for="size">Generate:</label>
    <input type="text" id="size">
    <label for="size">numbers</label>
    <br><br>
    <label for="Sort">Sort numbers:</label>
    <select id="Sort">
      <option value="Do not sort">Do not sort</option>
      <option value="Ascending">Ascending</option>
      <option value="Descending">Descending</option>
    </select>
    <br><br>
    <label for="Duplicates">Allow Duplicates:</label>
    <select id="Duplicates">
      <option value="No">No</option>
      <option value="Yes">Yes</option>
    </select>
    <br><br>
    <button onclick="func()">Generate</button>
    <br><br>
    <span id="result"></span>
  </div>
</body>
<script>
  function func() {
    //Inputs
    var min = parseInt(document.getElementById('Min').value);
    var max = parseInt(document.getElementById('Max').value);
    var sort = document.getElementById('Sort');
    var duplicate = document.getElementById('Duplicates');
    var size = document.getElementById('size').value;
    var result = document.getElementById('result');
    const rand = [];
    for (var i = 0; i <= size - 1; i++) {
      rand.push(Math.floor(Math.random() * max) + min);
    }
    if (sort.value == "Ascending") {
      rand.sort(function(a, b) {
        return a - b
      });
      result.innerHTML = rand;
      let unique = [...new Set(rand)];
      console.log(unique)
    } else if (sort.value == "Descending") {
      rand.sort(function(a, b) {
        return b - a
      });
      result.innerHTML = rand;
    } else if (sort.value == "Do not sort") {
      result.innerHTML = rand;
    }
  }
</script>

</html>

Does this answer your question? [Get all unique values in a JavaScript array (remove duplicates)](https://stackoverflow.com/questions/1960473/get-all-unique-values-in-a-javascript-array-remove-duplicates) — Lazar Ljubenović, Feb 16 '20 at 15:13
Use a [`Set`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set) instead of an array. Set replaces a value if it already contains it, and it can be iterated over with a `for...of` loop. — Emiel Zuurbier, Feb 16 '20 at 15:15
btw, you need `rand.push(Math.floor(Math.random() * (max - min)) + min);` — Nina Scholz, Feb 16 '20 at 15:17
what should happen, if there are no values for filling the array? for example, you have 3 and 6 as min and max and you want 5 elements, but only 4 elements are possible? — Nina Scholz, Feb 16 '20 at 15:19
@LazarLjubenović, that is not a good dupe: the OP already removes duplicates using `Set`. — trincot, Feb 16 '20 at 15:24

Lonnie Best · Answer 1 · 2020-02-16T15:50:49.813

As you know, a Set doesn't allow duplicate values:

let ary = [1,1,2,2,3,3,4,4,5,5];
let set = new Set(ary);
let newAry = Array.from(set);
console.log(newAry); // outputs: [1,2,3,4,5]

You can get a set to contain the desired amount of numbers by using its size property:

function randomNumberBetween(iLowest,iHighest)
{
 var iChoices = iHighest - iLowest + 1;
 return Math.floor(Math.random() * iChoices + iLowest);
}

let max = 10;
let min = 1

let amountOfNumbers = max - min;
let set = new Set();

while (set.size < amountOfNumbers)
{
 set.add(randomNumberBetween(min,max));
}
console.log(Array.from(set));

However, it is more efficient to randomize an already existing array, because it avoids all the random duplicates rejected by the set:

function randomNumberBetween(iLowest,iHighest)
{
 var iChoices = iHighest - iLowest + 1;
 return Math.floor(Math.random() * iChoices + iLowest);
}

function randomizeArray(ary)
{
 var intialLength = ary.length;
 var aryNew = new Array();
 var iCurrent;
 while (aryNew.length < intialLength)
 {
  iCurrent = randomNumberBetween(0, ary.length - 1);
  aryNew.push(ary[iCurrent]);
  ary.splice(iCurrent, 1);
 }
 return aryNew;
}

let ary = [1,1,2,2,3,3,4,4,5,5];
let set = new Set(ary);
ary = Array.from(set);
let randomAry = randomizeArray(ary)
console.log(randomAry);

score 0 · Answer 2 · answered Feb 16 '20 at 15:20

Instead of producing random numbers independently, create an array with all values between min and max, shuffle it, and then pick the number of values from it that you need:

So replace this:

const rand = [];
for (var i = 0; i <= size - 1; i++) {
    rand.push(Math.floor(Math.random() * max) + min);
}

...with this:

const rand = shuffle(Array.from({length: max - min + 1}, (_, i) => i + min).slice(0, size);

You can take the shuffle function from this answer:

function shuffle(a) {
    var j, x, i;
    for (i = a.length - 1; i > 0; i--) {
        j = Math.floor(Math.random() * (i + 1));
        x = a[i];
        a[i] = a[j];
        a[j] = x;
    }
    return a;
}

Be aware that you cannot slice more values than that are present in the min-to-max array. There is of course no way to take 10 unique integers from the range [4...6].

How to replace duplicates from array

2 Answers2