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

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?

CodePudding user response：

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; }

CodePudding user response：

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/

CodePudding user response：

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 :| ...)

CodePudding user response：

Please try this one

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;
}