Transforming an array to a sorted object

Question

I have in input an array of arrays such as :

[
  [ '1', '12:23', '16:27' ],
  [ '1', '08:00', '17:59' ],
  [ '2', '14:50', '15:14' ],
  [ '2', '09:42', '11:00' ],
  [ '3', '17:16', '17:41' ],
  [ '3', '08:00', '17:59' ],
  [ '4', '08:10', '13:01' ],
]

I'd like to be able to use the first element of the arrays as a key object, to store the second and third element in it, sorted by the second one, as this :

  {
    1: [
      ['08:00', '17:59'],
      ['12:23', '16:27'],
    ],
    2: [
      ['09:42', '11:00'],
      ['14:50', '15:14'],
    ]
    3: [
      ['08:00', '17:59'],
      ['17:16', '17:41'],
    ]
    4: [
      ['08:10', '13:01'],
    ]      
  }

Hints?

Answer 1

Converting an array into an object is an ideal candidate for using Array.prototype.reduce() :

const arr = [
  [ '1', '12:23', '16:27' ],
  [ '1', '08:00', '17:59' ],
  [ '2', '14:50', '15:14' ],
  [ '2', '09:42', '11:00' ],
  [ '3', '17:16', '17:41' ],
  [ '3', '08:00', '17:59' ],
  [ '4', '08:10', '13:01' ],
];

const obj = arr.reduce((acc, item) => {
  const [key, timeA, timeB] = item;
  
  // create array of time pairs if necessary
  acc[key] = acc[key] || [];
  
  // add time pairs to array
  acc[key].push([timeA, timeB]);
  
  return acc;
}, {});

// sort the time pair arrays by the first time
const compare = (a, b) => {
  const aTime = a[0],
    bTime = b[0];
  return aTime.localeCompare(bTime);
};
Object.values(obj).forEach(arr => {
  arr.sort(compare);
});

document.querySelector('pre').innerText = 'obj ' +
  JSON.stringify(obj, null, 2);

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