CODEWITHSUNDEEP
javascript
WebArtisan
WebArtisan

Reputation: 4227

Add a random and not existing item to array from another array

Let's assume we have an array of items:

const arr1 = [22, 54, 67, 11, ...so on]

and empty one:

let arr2 = []

I can add random item with:

arr2 = [...arr2, arr1[Math.floor(Math.random()*arr1.length)]]

BUT how can I add a random item from first array to 2nd and already added should not be added?

Yes, we can keep added indexes in some tmp variable, but it doesnt seems right and I think there should be a different solution.

NOTE: array spreads because I need to add an item with some events. For example user click to button and new item will be added to 2nd array, and this array may contain already added elems

Upvotes: 0

Views: 94

Answers (7)

hygull
hygull

Reputation: 8740

@WebArtisan, you can also try the below code.

// Function that returns a randomly selected unique list of items from another 
// array with duplicated items
function getUniqueRandomItems(arr1) {
	let arr2 = [];

	while(arr1.length) {
		// A random number in range [0, arr1.length-1]
		randomIndex = Math.floor((Math.random() * (arr1.length)) + 1) - 1; 

		// Removing 1 item from random index in range
		removedItem = arr1.splice(randomIndex, 1)[0]; 
		
		// If removedItem does not exist then add it to arr1
		if(arr2.indexOf(removedItem) < 0) {
		    arr2.push(removedItem);  
		}
	}

	return arr2 // Return the result array with unique random items
}

/************ TEST 1****************************************/
const arr1 = [22, 54, 67, 11, 54, 22, 67, 11, 88, 90, 54, 2, 3, 2, 11, 54, 0];
const arr2 = getUniqueRandomItems(arr1);
console.log(arr2); // [ 2, 22, 88, 67, 54, 11, 3, 90, 0 ]

/************ TEST 2****************************************/
const arr3 = [1, 5, 2, 5, 1, 3, 3, 6, 3, 1, 9, 8, 10, 9, 7, 4, 3, 4, 2, 1, 10];
const arr4 = getUniqueRandomItems(arr3);
console.log(arr4); // [ 1, 7, 9, 10, 5, 3, 2, 8, 4, 6 ]

Upvotes: 0

sjahan
sjahan

Reputation: 5940

If this is ok to mutate arr1 (as Matt Burland suggested in comments), try this:

arr2 = [...arr2, ...arr1.splice(Math.floor(Math.random()*arr1.length), 1]);

splice will remove the item from arr1 and return you the item removed, ready to be added in arr2!

If you cannot change it, just make a clone before using this line!

Hoping this will help you :)

Upvotes: 1

Nicolas
Nicolas

Reputation: 8650

You could use the include function on your second array and check if the element you are trying to add does not exists.

let randomItem = arr1[Math.floor(Math.random()*arr1.length)];
while(arra2.includes(randomItem)) {
    randomItem = arr1[Math.floor(Math.random()*arr1.length)];
}
arr2.push(randomItem);

Upvotes: 0

nick
nick

Reputation: 2853

Something like this should work

let arr1 = [22,43,67,11,63];
let indexes = [...arr1.keys()];
indexes = indexes.sort(() => Math.Random() - 0.5);
let arr2 = [];
arr2 = [...arr2, arr1[indexes.pop()]]

This lets you preserve the original order of your first array too.

Upvotes: 0

Darkrum
Darkrum

Reputation: 1373

If compatibility is not an issue you can use array set.

var arr1 = [44, 55, 100];
var arr2 = [44, 55, 100];

var arr3 = [...new Set(arr1, arr2)];

Upvotes: 0

Niladri Basu
Niladri Basu

Reputation: 10614

I think you are looking for something like this: 

const arr1 = [22, 54, 67, 11, 23, 56, 43, 77, 34, 76, 30]

let arr2  = []


function addRandom() {

  if(new Set(arr1).size === arr2.length) return;  //prevention from infinite loop
  // if(arr1.length=== arr2.length) return;  // if arr1 doesn't contain duplicates
  let random = arr1[Math.floor(Math.random()*arr1.length)];
  if (!arr2.includes(random)) {
    arr2.push(random);
  } else {
    addRandom();
  }
}

addRandom();
console.log(arr2);

addRandom();
console.log(arr2);

addRandom();
console.log(arr2);

If you are sure that arr1 wont contain duplicates then replace (new Set(arr1).size === arr2.length) with arr1.length=== arr2.length.

Upvotes: 1

Ankit Agarwal
Ankit Agarwal

Reputation: 30739

You can create your custom logic to push the random value in arr2 so that the condition is that the numbers must be unique in arr2 and it will have maximum random numbers till the length of arr1:

const arr1 = [27, 54, 67, 11, 15, 22, 26, 58, 45, 87];
let arr2 = [];

function getRandom(){
  var randomNumber = arr1[Math.floor(Math.random()*arr1.length)];
  while(arr2.indexOf(randomNumber) !== -1 && arr2.length !== arr1.length) {
    randomNumber = arr1[Math.floor(Math.random()*arr1.length)];
  }
  arr2.push(randomNumber);
}
getRandom(); getRandom(); getRandom(); getRandom(); getRandom(); getRandom(); getRandom(); getRandom(); getRandom(); getRandom();getRandom();
console.log(arr2);

Upvotes: 1

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