Randomly divide an array of objects into two equal arrays

Question

Randomly divide an array of objects into two equal arrays

I am facing a challenge with an array of objects;

let persons = [
    {id: 1, name: "..."},
    {id: 2, name: "..."},
    {id: 3, name: "..."},
    {id: 4, name: "..."},
    {id: 5, name: "..."},
    {id: 6, name: "..."},
    {id: 7, name: "..."},
    {id: 8, name: "..."}
]

My goal is to divide this array into two equal-length arrays and have different random data in each array every time the function is executed, not the same set of objects.

I attempted to achieve this using the following function:

function splitArr(data, part) {
    let list1 = [];
    let list2 = [];
    for(let i = 0; i < data.length ; i++) {
        let random = Math.floor(Math.random() * data.length);
        if(random % 2 === 0) {
            list1.push(data[i]);
        } else {
            list2.push(data[i]);
        }

    }
    return [list1, list2];
}

However, it is not guaranteed that the function will always return two arrays of equal length. Sometimes it returns arrays with 2 and 6 elements, which is not what I intended.

https://i.sstatic.net/QLzk2.png

javascript arrays

Answer 1

Answer №1

To divide an array in half, first randomly shuffle the elements of the array.

Here is a function for shuffling an array, which can be found here:

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;
}

To split the shuffled array into two lists:

let list2 = shuffle([...data]); // spreading to avoid changing the original
let list1 = list2.splice(0, data.length >> 1);

The shift operator >> is used to obtain the truncated half of the array length.

Answer 2

To divide an array in half, first randomly shuffle the elements of the array.

Here is a function for shuffling an array, which can be found here:

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;
}

To split the shuffled array into two lists:

let list2 = shuffle([...data]); // spreading to avoid changing the original
let list1 = list2.splice(0, data.length >> 1);

The shift operator >> is used to obtain the truncated half of the array length.

Answer 3

Answer №2

In my opinion, the most efficient and reliable approach would be utilizing native array methods in this scenario. I highly suggest implementing the slice method as demonstrated below:

function separateArray(data) {
  const arrayLength = data.length;

  const firstHalf = data.slice(0, arrayLength/2);
  const secondHalf = data.slice(arrayLength / 2, arrayLength);

  return [firstHalf, secondHalf];
}

This function provides a versatile solution that consistently yields two arrays of equal length. For special cases involving arrays with odd lengths, consider experimenting with Math.min() and Math.ceil.

Answer 4

In my opinion, the most efficient and reliable approach would be utilizing native array methods in this scenario. I highly suggest implementing the slice method as demonstrated below:

function separateArray(data) {
  const arrayLength = data.length;

  const firstHalf = data.slice(0, arrayLength/2);
  const secondHalf = data.slice(arrayLength / 2, arrayLength);

  return [firstHalf, secondHalf];
}

This function provides a versatile solution that consistently yields two arrays of equal length. For special cases involving arrays with odd lengths, consider experimenting with Math.min() and Math.ceil.

Answer 5

Answer №3

To effortlessly achieve this task, consider utilizing randojs.com. The randoSequence function is particularly useful as it does not impact the original array. Afterwards, utilize the slice function to divide the arrays and employ the bitwise operator >> for handling arrays with an odd length.

function shuffleAndSplit(arr){
  var shuffled = randoSequence(arr);
  shuffled.forEach((item, i) => {shuffled[i] = item.value;});
  return [shuffled.slice(0, shuffled.length >> 1), shuffled.slice(shuffled.length >> 1)];
}

console.log(shuffleAndSplit(["a", "b", "c", "d", "e", "f", "g"]));

<script src="https://randojs.com/1.0.0.js"></script>

If you wish to simplify further while disregarding Internet Explorer compatibility issues, consider using the map function. Here's a variation of the previous code snippet that utilizes map:

function shuffleAndSplit(arr){
  var shuffled = randoSequence(arr).map(item => item.value);
  return [shuffled.slice(0, shuffled.length >> 1), shuffled.slice(shuffled.length >> 1)];
}

console.log(shuffleAndSplit(["a", "b", "c", "d", "e", "f", "g"]));

<script src="https://randojs.com/1.0.0.js"></script>

Answer 6

To effortlessly achieve this task, consider utilizing randojs.com. The randoSequence function is particularly useful as it does not impact the original array. Afterwards, utilize the slice function to divide the arrays and employ the bitwise operator >> for handling arrays with an odd length.

function shuffleAndSplit(arr){
  var shuffled = randoSequence(arr);
  shuffled.forEach((item, i) => {shuffled[i] = item.value;});
  return [shuffled.slice(0, shuffled.length >> 1), shuffled.slice(shuffled.length >> 1)];
}

console.log(shuffleAndSplit(["a", "b", "c", "d", "e", "f", "g"]));

<script src="https://randojs.com/1.0.0.js"></script>

If you wish to simplify further while disregarding Internet Explorer compatibility issues, consider using the map function. Here's a variation of the previous code snippet that utilizes map:

function shuffleAndSplit(arr){
  var shuffled = randoSequence(arr).map(item => item.value);
  return [shuffled.slice(0, shuffled.length >> 1), shuffled.slice(shuffled.length >> 1)];
}

console.log(shuffleAndSplit(["a", "b", "c", "d", "e", "f", "g"]));

<script src="https://randojs.com/1.0.0.js"></script>

Answer 7

Answer №4

If you're looking to divide it into two separate parts, consider using the splice method.

This method takes two parameters (three if replacing elements): the starting index for splicing and the number of elements to remove. It will return the removed elements, effectively splitting your array in half. By removing elements from the original array, you'll end up with two arrays of equal length (especially when dealing with an even number of elements).

To add randomness to your array before splitting it, you can simply shuffle it beforehand. Below is an example leveraging a function from Jeff's answer:

/**
 * https://stackoverflow.com/a/6274381/5784924
 * Shuffles array in place. ES6 version
 * @param {Array} a items An array containing the items.
 */
function shuffle(a) {
    for (let i = a.length - 1; i > 0; i--) {
        const j = Math.floor(Math.random() * (i + 1));
        [a[i], a[j]] = [a[j], a[i]];
    }
    return a;
}

let persons = shuffle([
    {id: 1, name: "..."},
    {id: 2, name: "..."},
    {id: 3, name: "..."},
    {id: 4, name: "..."},
    {id: 5, name: "..."},
    {id: 6, name: "..."},
    {id: 7, name: "..."},
    {id: 8, name: "..."}
]);

let firstArray = persons.splice(0, persons.length / 2);
console.log(firstArray.map((item) => item.id), persons.map((item) => item.id));

Answer 8

If you're looking to divide it into two separate parts, consider using the splice method.

This method takes two parameters (three if replacing elements): the starting index for splicing and the number of elements to remove. It will return the removed elements, effectively splitting your array in half. By removing elements from the original array, you'll end up with two arrays of equal length (especially when dealing with an even number of elements).

To add randomness to your array before splitting it, you can simply shuffle it beforehand. Below is an example leveraging a function from Jeff's answer:

/**
 * https://stackoverflow.com/a/6274381/5784924
 * Shuffles array in place. ES6 version
 * @param {Array} a items An array containing the items.
 */
function shuffle(a) {
    for (let i = a.length - 1; i > 0; i--) {
        const j = Math.floor(Math.random() * (i + 1));
        [a[i], a[j]] = [a[j], a[i]];
    }
    return a;
}

let persons = shuffle([
    {id: 1, name: "..."},
    {id: 2, name: "..."},
    {id: 3, name: "..."},
    {id: 4, name: "..."},
    {id: 5, name: "..."},
    {id: 6, name: "..."},
    {id: 7, name: "..."},
    {id: 8, name: "..."}
]);

let firstArray = persons.splice(0, persons.length / 2);
console.log(firstArray.map((item) => item.id), persons.map((item) => item.id));

Answer 9

Answer №5

the issue with the current method is as follows:

if(random % 2 === 0) {
    list1.push(data[i]);
} else {
    list2.push(data[i]);
}

attempting to insert into a random array without considering if both arrays are of equal length poses a problem (maintaining true randomness will be difficult).

it would be more effective to randomly insert items into each array during every iteration.

let persons = [
    {id: 1, name: "..."},
    {id: 2, name: "..."},
    {id: 3, name: "..."},
    {id: 4, name: "..."},
    {id: 5, name: "..."},
    {id: 6, name: "..."},
    {id: 7, name: "..."},
    {id: 8, name: "..."}
]
function splitArr(data, part) {
    let list1 = [];
    let list2 = [];
    let isPair = false;
    
    while(data.length > 0){
      const randomEntry = Math.floor(Math.random() * data.length);
      const arrayToPush = isPair?list1:list2;
      arrayToPush.push(data[randomEntry]);
      data.splice(randomEntry, 1);
      isPair = !isPair;
    }
    console.log(list1.length, list2.length)
    return [list1, list2];
}

splitArr(persons)

Answer 10

the issue with the current method is as follows:

if(random % 2 === 0) {
    list1.push(data[i]);
} else {
    list2.push(data[i]);
}

attempting to insert into a random array without considering if both arrays are of equal length poses a problem (maintaining true randomness will be difficult).

it would be more effective to randomly insert items into each array during every iteration.

let persons = [
    {id: 1, name: "..."},
    {id: 2, name: "..."},
    {id: 3, name: "..."},
    {id: 4, name: "..."},
    {id: 5, name: "..."},
    {id: 6, name: "..."},
    {id: 7, name: "..."},
    {id: 8, name: "..."}
]
function splitArr(data, part) {
    let list1 = [];
    let list2 = [];
    let isPair = false;
    
    while(data.length > 0){
      const randomEntry = Math.floor(Math.random() * data.length);
      const arrayToPush = isPair?list1:list2;
      arrayToPush.push(data[randomEntry]);
      data.splice(randomEntry, 1);
      isPair = !isPair;
    }
    console.log(list1.length, list2.length)
    return [list1, list2];
}

splitArr(persons)

Answer 11

Answer №6

Would you find this solution beneficial?


function shuffleArray(data, numberOfDecks) {
  data = data.slice();
  const decks = [];
  let i = 0;
  while (data.length) {
    if (!Array.isArray(decks[i])) decks[i] = [];
    decks[i].push(data.splice(Math.random()*data.length, 1)[0]);
    i = (i+1) % numberOfDecks;
  }
  return decks;
}

shuffleArray(players, 4) // specifying 4 for four decks

Answer 12

Would you find this solution beneficial?


function shuffleArray(data, numberOfDecks) {
  data = data.slice();
  const decks = [];
  let i = 0;
  while (data.length) {
    if (!Array.isArray(decks[i])) decks[i] = [];
    decks[i].push(data.splice(Math.random()*data.length, 1)[0]);
    i = (i+1) % numberOfDecks;
  }
  return decks;
}

shuffleArray(players, 4) // specifying 4 for four decks

Randomly divide an array of objects into two equal arrays

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

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