How to split an array into even length chunks?

Question

I want to split an array in even (or as even as possible) chunks. The input of the function should be the array and the size of the chunks. Say you have the array

[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]

If you put it in the function below, with 5 as chunk size, it will result in the following

[[1,2,3,4,5],[6,7,8,9,10],[11,12,13,14,15],[16,17]

However, I want the result to be

[[1,2,3,4,5],[6,7,8,9],[10,11,12,13],[14,15,16,17]

Which means sacrificing the length of the arrays before to make them only differ one in length.

The function I'm currently using is stated below. I've tried various things with modulo but I can't figure it out.

function chunkArray(myArray, chunkSize){
var arrayLength = myArray.length;
var tempArray = [];

for (index = 0; index < arrayLength; index += chunkSize) {
    myChunk = myArray.slice(index, index+chunkSize);
    // Do something if you want with the group
    tempArray.push(myChunk);
}

return tempArray;

}

Why is the length of the second chunk 4? Whats the rule behind it? — Jonas Wilms, Jul 05 '19 at 14:22
what is expected , if the last array has only 2 elements left, any squenece or order?please provide possible scenarios — Naga Sai A, Jul 05 '19 at 14:25

score 1 · Accepted Answer · answered Jul 05 '19 at 14:35

1

With this solution you get evenly split array items until the last item which incorporates any left over items (collection of items that's length is less than the chunk size.)

const a = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]
const chunk = 4

const chunk_array = (a, c) => {
  let arr = []
  
  a.forEach((_, i) => {
    if (i%chunk === 0) arr.push(a.slice(i, i+chunk))
  })
  
  const [left_overs] = arr.filter(a => a.length < chunk)
  
  arr = arr.filter(a => a.length >= chunk)
  
  arr[arr.length-1] = [...arr[arr.length-1], ...left_overs] 
  
  return arr
}

console.log(
  chunk_array(a, chunk)
)

answered Jul 05 '19 at 14:35

Francis Leigh

1,870
10
25

one more case to add should be what if number of chunks is more then 1/2 of array length – Rinor Dreshaj Jul 05 '19 at 14:40
Good idea and if it is greater than 1/2 of the original length we just keep the `left_over` array on its own? @RinorDreshaj – Francis Leigh Jul 05 '19 at 14:43
well I suppose if the left over size is < then 1/2 of actual chunk size just inlcude in that array, but in this case if chunk size is 10, we can have 2 arrays one of size 10 and the other 7, but if size is like 15 I think you should stick with one array rather then creating another array of size 2 – Rinor Dreshaj Jul 05 '19 at 14:46
I will have to do that later. gotta go! Feel free to make an edit :-) – Francis Leigh Jul 05 '19 at 14:51
Good job btw – Rinor Dreshaj Jul 05 '19 at 14:51

Flo · Answer 2 · 2019-07-05T14:33:57.287

-1

You could check with a modulo if your array length is odd :

let MY_CHUNK_CONST = 5
let first_chunk_size = MY_CHUNK_CONST,
other_chunk_size = MY_CHUNK_CONST;
let myArray = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17];
modulo_res = myArray.length % 2; // 0 if even 1 if odd

if(modulo_res){
 other_chunk_size = first_chunk_size - 1;
}

var tempArray = [];

myChunk = myArray.slice(0, 0+first_chunk_size);
tempArray.push(myChunk);
for (index = 1; index < myArray.length; index += other_chunk_size) {
    myChunk = myArray.slice(index, index+other_chunk_size);
    // Do something if you want with the group
    tempArray.push(myChunk);
}

console.log(tempArray)
// [[1,2,3,4,5],[6,7,8,9],[10,11,12,13],[14,15,16,17]

Hope it helps.

edited Jul 05 '19 at 14:33

answered Jul 05 '19 at 14:24

Flo

936
1
8
19

Odd in the sense of "not all chunks have equal size" – Jonas Wilms Jul 05 '19 at 14:25
5 in OP is just an example number, he don't want to make 5 chunk. OP want to create equal number of chunks based on array size. – ravibagul91 Jul 05 '19 at 14:32
Yeah that's why I use 5. He then is able to decide which value he wants to put instead. – Flo Jul 05 '19 at 14:34

score -1 · Answer 3 · answered Jul 05 '19 at 14:24

-1

My solution!

const chunk = (arr, chunkSize) => {
  let chunked = [];
  for (let i = 0; i< arr.length; i+=chunkSize){
    chunked.push(
      arr.slice(i, (i + chunkSize))
    );
  }

  return chunked;
};

const data = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17];

console.log(chunk(data, 5));
// returns [[1,2,3,4,5],[6,7,8,9,10],[11,12,13,14,15],[16,17]]

answered Jul 05 '19 at 14:24

StefanN

871
6
19

5 in OP is just an example number, he don't want to make 5 chunk. OP want to create equal number of chunks based on array size. – ravibagul91 Jul 05 '19 at 14:31

How to split an array into even length chunks?

3 Answers3