Javascript - How do I map an array of objects to a datatable with column names?

Question

I have some data like this, an array of objects:

source = [{
  day: 1,
  deliveries: 16,
  hours: 9
}, {
  day: 2,
  deliveries: 19,
  hours: 11
}]

Which I would like to have in this format:

source = (['day', 'deliveries', 'hours'],
          ['1', '16', '9'],
          ['2', '19', '11'])

Sort of like a table. I read up a little on mapping arrays and tried this:

const datatable = source.map(d => Array.from(Object.keys(d)))
console.log(datatable)
// [["day", "deliveries", "hours"], ["day", "deliveries", "hours"]]

And this:

const datatable = source.map(d => Array.from(Object.values(d)))
console.log(datatable)
// [[1, 16, 9], [2, 19, 11]]

Each gives me half of what I want. I tried this:

let datatable = source.map(d => Array.from(Object.keys(d)))
let datatable2 = source.map(d => Array.from(Object.values(d)))

datatable = datatable[1]
let combined = datatable.concat(datatable2);
console.log(combined)
///["day", "deliveries", "hours", [1, 16, 9], [2, 19, 11]]

But even here the column names are not being combined correctly, and this way seems a little messy. How do I have the keys be on top (like column names would be) and the values following them?

Answer 1

Assuming you want source to be an array of arrays (common for table-like structures), get the keys once, then add each row array mapping the object's properties to the key for that index:

const keys = Object.keys(source[0]);
const result = [keys, ...source.map(obj => keys.map(key => obj[key]))];

Live Example:

const source = [{
  day: 1,
  deliveries: 16,
  hours: 9
}, {
  day: 2,
  deliveries: 19,
  hours: 11
}];

const keys = Object.keys(source[0]);
const result = [keys, ...source.map(obj => keys.map(key => obj[key]))];
console.log(result);

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

Note that this assumes a couple of things:

1. The source array always has at least one object in it.
2. The objects in the source array all have the same set of properties.
3. You want the keys to be in the order in which they appear in the first object in the array. (JavaScript object properties do have a defined order now, but using that order is almost never a good idea, so you might want to do some kind of sort operation on keys.)