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

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?

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Answer

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 }));
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