javascriptlodash

lodash chunk from end of array

I have an array

const myArray = [1, 2, 2, 2, 3, 3, 3, 4, 4, 4];

that I want to split into smaller arrays. I am using lodash chunk to do it.

_.chunk(myArray, 3);

this will return

[1, 2, 2], [2, 3, 3], [3, 4, 4], [4]

but I would like it to return

[1], [2, 2, 2], [3, 3, 3], [4, 4, 4]

my solution was this

_.chain(myArray).reverse().chunk(3).reverse().value()

it reverses the array, splits it and then reverses it again. But is there a better way to do this? So chunk starts from the end and not the start.

Runnable example:

const myArray = [1, 2, 2, 2, 3, 3, 3, 4, 4, 4];

console.log(_.chunk(myArray, 3));
  // => [1, 2, 2], [2, 3, 3], [3, 4, 4], [4]

console.log(_.chain(myArray).reverse().chunk(3).reverse().value());
  // => [1], [2, 2, 2], [3, 3, 3], [4, 4, 4]
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.js"></script>

Solution

  • Find the remainder, and if there's remainder, slice it from the left side, and combine it with the chunks of the rest of the array. If no remainder, chunk normally:

    const myArray = [1, 21, 22, 23, 31, 32, 33, 41, 42, 43];

const chunkRight = (arr, size) => {
  const rm = arr.length % size;
  
  return rm ?
    [arr.slice(0, rm), ..._.chunk(arr.slice(rm), size)]
    :
    _.chunk(arr, size);
};

const result = chunkRight(myArray, 3);

console.log(result);
    <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.js"></script>