Split one array into multiple arrays based on index with Javascript [duplicate]

Question

I have an array like this

var arr = ['2021-07-09T00:00:00Z','9242.80','4316.91','32557.90','14687.00','2021-07-10T00:00:00Z','9242.80','4316.91','32557.90','14687.00','2021-07-11T00:00:00Z','9242.80','4316.91','32557.90','14687.00','2021-07-12T00:00:00Z','9242.80','4316.91','32557.90','14687.00']

I'd like to make 4 different arrays from this one array (either by the date or the order of the items (so after every 5 items it creates a new array. I haven't been able to work it out even after searching. Could someone please point me in the right direction?

Does this answer your question? How I can split my array to multiple arrays based in a value with Javascript? — TBA
– TBA, Commented Oct 24, 2021 at 9:44

DecPK · Accepted Answer · 2021-10-24 09:50:59Z

You can use reduce here to achieve the desired result.

var arr = [
  "2021-07-09T00:00:00Z",
  "9242.80",
  "4316.91",
  "32557.90",
  "14687.00",
  "2021-07-10T00:00:00Z",
  "9242.80",
  "4316.91",
  "32557.90",
  "14687.00",
  "2021-07-11T00:00:00Z",
  "9242.80",
  "4316.91",
  "32557.90",
  "14687.00",
  "2021-07-12T00:00:00Z",
  "9242.80",
  "4316.91",
  "32557.90",
  "14687.00",
];

const result = arr.reduce((acc, curr, i) => {
  if (i % 5 !== 0) acc[acc.length - 1].push(curr);
  else acc.push([curr]);

  return acc;
}, []);

console.log(result);

/* This is not a part of answer. It is just to give the output fill height. So IGNORE IT */
.as-console-wrapper { max-height: 100% !important; top: 0; }

You can also generalize the function as:

var arr = [
  "2021-07-09T00:00:00Z",
  "9242.80",
  "4316.91",
  "32557.90",
  "14687.00",
  "2021-07-10T00:00:00Z",
  "9242.80",
  "4316.91",
  "32557.90",
  "14687.00",
  "2021-07-11T00:00:00Z",
  "9242.80",
  "4316.91",
  "32557.90",
  "14687.00",
  "2021-07-12T00:00:00Z",
  "9242.80",
  "4316.91",
  "32557.90",
  "14687.00",
];

function splitArrayAfter(arr, num) {
  return (result = arr.reduce((acc, curr, i) => {
    if (i % num !== 0) acc[acc.length - 1].push(curr);
    else acc.push([curr]);

    return acc;
  }, []));
}

console.log(splitArrayAfter(arr, 5));

/* This is not a part of answer. It is just to give the output fill height. So IGNORE IT */
.as-console-wrapper { max-height: 100% !important; top: 0; }

Majed Badawi · Accepted Answer · 2021-10-24 09:53:37Z

Using Array#reduce, you can iterate over the array. At every iteration, we add a new array if we're just starting (i.e. no sub-arrays), the element is a date, or we've reached 5 elements. Otherwise, add the element to the latest sub-array:

const arr = ['2021-07-09T00:00:00Z', '9242.80', '4316.91',  '32557.90', '14687.00',  '2021-07-10T00:00:00Z', '9242.80', '4316.91', '32557.90', '14687.00', '2021-07-11T00:00:00Z', '9242.80', '4316.91', '32557.90', '14687.00', '2021-07-12T00:00:00Z', '9242.80', '4316.91', '32557.90', '14687.00'];

const res = arr.reduce((list, e) => {
  if(Date.parse(e) || list.length === 0 || list[list.length-1].length === 5) {
    list.push([e]);
  } else {
    list[list.length-1].push(e);
  }
  return list;
}, []);

console.log(res);

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