Chunk an array of objects and add empty arrays at the end

Question

I need to chunk an array of objects so i write:

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

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


    return output
}

and it works fine if I have rules like { 0: 2, 1: 2 }

 const input = [[1,2,3],[4,5,6,7]],
                output = conditionalChunk(input.flat(), 3, { 0: 2, 1: 2 });
          
    // OUTPUT: [[1,2],[3,4],[5,6,7]]

but when I have rules at the end like { 0: 2, 1: 2, 2:0, 5:0 } my function ignore to create empty arrays at the end.

the output I need is:

const input = [[1,2,3],[4,5,6,7]],
                    output = conditionalChunk(input.flat(), 3, { 0: 2, 1: 2, 2:0, 5:0 });
              
        // OUTPUT: [[1,2],[3,4],[],[5,6,7],[]]

so I just need to not ignore rules for empty arrays at the end of array. How I can do that?

it should be add at the end of array as empty, not need to be at position 5 — Aleks Per
– Aleks Per, Commented Jul 27, 2022 at 15:33
in rule, it could be also 4 or any larger value to get an empty array at the end, right? — Nina Scholz
– Nina Scholz, Commented Jul 27, 2022 at 15:37
Your code is actually working as intended. The problem with needing empty arrays after copy is empty is a function call like const input = [[1,2,3],[4,5,6,7]], output = conditionalChunk(input.flat(), 3, { 0: 2, 1: 2, 2:0, 7:0 }); would now be legitimate — user14459251
– user14459251, Commented Jul 27, 2022 at 15:44

Nina Scholz · Accepted Answer · 2022-07-27 16:27:57Z

1

Finally, you could check the keys of rules and if greater or equal to the next index of output push an empty array.

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

    while (i < array.length)
        output.push(array.slice(i, i += rules[output.length] ?? size));
    
    let l = Object.keys(rules).reduce((l, v) => l + (v >= output.length), 0);

    while (l--) output.push([]);

    return output;
}

console.log(conditionalChunk([1, 2, 3, 4, 5, 6, 7], 3, { 0: 2, 1: 2 })); // [[1,2],[3,4],[5,6,7]]
console.log(conditionalChunk([1, 2, 3, 4, 5, 6, 7], 3, { 0: 2, 1: 2, 2: 0, 5: 0 })); // [[1,2],[3,4],[],[5,6,7],[]]
console.log(conditionalChunk([1, 2, 3, 4, 5, 6, 7], 3, { 0: 0, 1: 2, 8: 0, 7: 0, 9:0, 20:0 }));

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Jul 27, 2022 at 16:27

answered Jul 27, 2022 at 15:31

Nina Scholz

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Comments

edyrkaj · Accepted Answer · 2022-07-27 15:48:17Z

0

maybe you can try this, I prefer for...each loop in place of a while.

function conditionalChunk(array, size = 1, rules = {}) {
    let copy = [...array],
        output = [],
        i = 0;


        for (const rule of Object.keys(rules)) {
            let val = copy.splice(0, rules[rule] || size);
      if (typeof val === 'undefined') val = [];
      
      output.push(val);
    }

    return output;
}

var results = conditionalChunk([1, 2, 3, 4, 5], 2, { 0:2, 1: 2, 2:2, 3:0 });

console.log(results, '::results::');

https://jsfiddle.net/5ozbj7na/

answered Jul 27, 2022 at 15:48

edyrkaj

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2 Comments

Aleks Per Over a year ago

Code dont work for rules like: var results = conditionalChunk([1, 2, 3, 4, 5], 2, { 0:0, 1: 2, 2:2, 11:0, 10:0 }); ... seems that do not create empty at the start ...

user14459251 Over a year ago

This wont work when rules is empty

user14459251 · Accepted Answer · 2022-07-27 16:17:32Z

0

A solution to your problem would be to add this bit of code after the while loop before the return statement

output.length = Math.max.apply(null, [output.length, ...Object.keys(rules)]) || output.length;
    
for (r in rules)
{
    output[r] = new Array(rules[r]);
}

It just extends the output array to the desired length then populates required spots with empty arrays (sorry for the complicated first line but JavaScript is complicated so :| ...)

answered Jul 27, 2022 at 16:17

user14459251

3 Comments

Aleks Per Over a year ago

I will test now

user14459251 Over a year ago

@AleksPer sure thing. I hope it works (at least on my end it does)

Aleks Per Over a year ago

console.log(conditionalChunk([1, 2, 3, 4, 5, 6, 7], 3, { 0: 0, 1: 2, 8: 0, 7: 0, 9:0, 20:0 }));

Jose Aviles · Accepted Answer · 2022-07-27 16:31:41Z

0

Please try this one, this should work for you and is done based on your solution, so it should be easier to understand

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

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

  const arr = Object.keys(rules).filter((key) => key > i);

  arr.forEach((key) => {
    if (rules[key] === 0) output.push([]);
  });

  return output;
}

edited Jul 27, 2022 at 16:31

answered Jul 27, 2022 at 16:28

Jose Aviles

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