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, Aug 03 '21 at 06:21
You are creating only one `temparray` in he very beginning and then overwriting its elements and pushing the same array multiple times — derpirscher, Aug 03 '21 at 06:22

Behemoth · Answer 1 · 2021-08-03T06:30:49.560

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]]

score 4 · Answer 2 · answered Aug 03 '21 at 06:37

@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));

score 3 · Answer 3 · edited Aug 03 '21 at 10:46

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 ]]

push() method not working properly in JavaScript

3 Answers3