push() method not working properly in JavaScript

Question

I'm trying to write a quite simple program that divides an array in another array of defined size smaller arrays, however the push() method is not working. Could someone please help me with it?

function chunk(array, size) {
  var newArray = [];
  var tempArray = [];

  for (let i = 0; i < array.length / size; i++) {
    for (let j = size * i, k = 0; j < size * i + size; j++, k++)
      tempArray[k] = array[j];

    newArray.push(tempArray);
  }

  return newArray;
}

var data = [1, 2, 3, 4, 5, 6, 7, 8];

console.log(chunk(data, 2));

The ideal output should be [[1, 2],[3, 4], [5, 6], [7, 8]]. However im getting [[7,8],[7,8],[7,8],[7,8]].

move var tempArray = []; inside of your first for loop. Currently, you're pushing the same array reference each time, and so modifications to it will impact it within your array — Nick Parsons
– Nick Parsons, Commented Aug 3, 2021 at 6:21
You are creating only one temparray in he very beginning and then overwriting its elements and pushing the same array multiple times — derpirscher
– derpirscher, Commented Aug 3, 2021 at 6:22

Behemoth · Accepted Answer · 2021-08-03 06:30:49Z

6

You're almost there. Just move the tempArray definition inside your first for-loop. Otherwise you would be pushing the same array each time.

Working Example:

function chunk(array, size) {
  const newArray = [];

  for (let i = 0; i < array.length / size; i++) {
    const tempArray = [];
    for (let j = size * i, k = 0; j < size * i + size; j++, k++)
      tempArray[k] = array[j];

    newArray.push(tempArray);
  }

  return newArray;
};

const data = [1, 2, 3, 4, 5, 6, 7, 8];

console.log(chunk(data, 2)); // [[1, 2],[3, 4], [5, 6], [7, 8]]

edited Aug 3, 2021 at 6:30

answered Aug 3, 2021 at 6:25

Behemoth

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Comments

Rukshan Jayasekara · Accepted Answer · 2021-08-03 06:37:51Z

4

@Behemoth's answer is the correct one for the question. But if you want, you can take a slightly different approach like this to reach the solution as well.

function chunk(array, size){
    const newArray = [];
    let i,j;
    
    for (i = 0,j = array.length; i < j; i += size) {
      newArray.push(array.slice(i, i + size));
    }
    return newArray;
};

var data = [1, 2, 3, 4, 5, 6, 7 ,8];

console.log(chunk(data, 2));

answered Aug 3, 2021 at 6:37

Rukshan Jayasekara

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Comments

Muhammad Bilal Bangash · Accepted Answer · 2021-08-03 10:46:55Z

3

Slightly different solution than @Behemoth and @Rukshan

function chunk(array, size) {
  var newArray = [];
  var tempArray = [];

  for (let i = 0; i < array.length / size; i++) {

    for (let j = i; j < i + 1; j++) {
      for (let k = 0; k < size; k++) {
        if (array[size * j + k]) {
          tempArray.push(array[size * j + k]);
        }
      }
      newArray.push(tempArray);
      tempArray = [];
    }
  }
  return newArray;
};

var data = [1, 2, 3, 4, 5, 6, 7, 8];

console.log(chunk(data, 2));

The solution would be [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7, 8 ], [ 9 ] ] instead of [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7, 8 ]]

edited Aug 3, 2021 at 10:46

Muhammad Bilal Bangash

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answered Aug 3, 2021 at 7:36

Aniruddha Kanere

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