Chunk an array with custom size for some index in javascript

Question

I have an array-like:

[1,2,3,4,5,6,7]

and I want to split this array into groups so I write:

Object.defineProperty(Array.prototype, 'chunk_inefficient', {
  value: function(chunkSize) {
    var array = this;
    return [].concat.apply([],
      array.map(function(elem, i) {
        return i % chunkSize ? [] : [array.slice(i, i + chunkSize)];
      })
    );
  }
});

Using var pages = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].chunk_inefficient(3); I got arrays like:

[[1,2,3], [4,5,6], [7,8,9], [10]]; and all its ok.

How I can update my function to keep creating arrays like this but etc. 2nd array to create with 2 elements;

var choose_array = 2;
var choose_elements_in_array = 2;

based om this 2 variables I need to change 2nd array to contain only 2 elements so I need to get array like:

[[1,2,3], [4,5,6], [7,8], [9,10]];

if

 var choose_array = 1;
    var choose_elements_in_array = 2;

then array needs to be like:

[[1,2,3], [4,5], [6,7,8], [9,10]];

If it easier how to recreate array [[1,2,3], [4,5,6], [7,8,9], [10]]; to [[1,2,3], [4,5], [6,7,8], [9,10]]; based on my variables

var choose_array = 1;
        var choose_elements_in_array = 2;

adiga · Accepted Answer · 2021-07-02 11:01:48Z

2

You could use an additional rules object which has the custom chunk size for each index in the output. If it is not defined for that index, use the default chunk size:

function conditionalChunk(array, size, rules = {}) {
  let copy = [...array],
      output = [],
      i = 0;

  while (copy.length)
    output.push( copy.splice(0, rules[i++] ?? size) )

  return output
}

For the below rules object

{
   0: 4,
   1: 2
}

The output will be:

[[1, 2, 3, 4], [5, 6], [7, 8, 9], [10]]

Here's a snippet:

function conditionalChunk(array, size, rules = {}) {
  let copy = [...array],
      output = [],
      i = 0;

  while (copy.length)
    output.push( copy.splice(0, rules[i++] ?? size) )

  return output
}

console.log(  
  JSON.stringify( conditionalChunk([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 3, { 1: 2 }) ) 
)

console.log(
  JSON.stringify( conditionalChunk([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 3, { 0:4, 1:2 }) )
)

edited Jul 2, 2021 at 11:01

answered Jul 2, 2021 at 10:52

adiga

35.4k9 gold badges66 silver badges88 bronze badges

Sign up to request clarification or add additional context in comments.

10 Comments

Aleks Per Over a year ago

Thank you very much. Works very well. Please just a suggestion - WHat is I have an array like: [[1,2,3], [4,5,6], [7,8,9], [10]]; and I just want to change 2 arrays to contain 2 products?

adiga Over a year ago

@AleksPer are you always going to reduce the number of items in the array? Like, you only want to make it 2 and not 4.

Aleks Per Over a year ago

no, sometimes I want to reduce to 2 elements, sometimes I need 4

adiga Over a year ago

@AleksPer the simplest way is to call the above conditionalChunk with array.flat() as input array

Aleks Per Over a year ago

Sorry for boring you but what if I have an input array like: [{'page_layout': 1, 'theme': 0, 'items', [1,2,3]}, {'page_layout': 5, 'theme': 1, 'items', [4,5,6,7]}] ... because chunk is actually pages and I need to put more details before each chunk

|

Collectives™ on Stack Overflow

Chunk an array with custom size for some index in javascript

1 Answer 1

10 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

10 Comments

Your Answer

Sign up or log in

Post as a guest

Related