JavaScript, split object in 2, and push in array

February 17, 2022

I have an array of objects like this:

const arrayOfObjects = [
  { A: 1, B: 2, C: 3 },
  { A: 3, B: 4, C: 1 }
]

And another array which is called "headers"

const headers = [
  ['A', 'B'],
  ['C']
]

I have to create an array similar to the first one but, with those objects splited by what headers have in it’s arrays.

This should be the goal:

const result = [
  [
    { A: 1, B: 2 },
    { C: 3 }
  ],
  [
    { A: 3, B: 4 },
    { C: 1 }
  ]
]

I tried by doing a "base" array with:

const baseArray = []
headers.forEach((header) => {
  const objFromHeader = {};
  header.forEach((head) => {
    objFromHeader[head] = 0;
  });
    baseArray.push(objFromHeader);
});

That will give me the result array but with 0 values for each key.

And then loop for the first array and put inside another array the base array with the correct values.

Then I wanted to fill each key according to the value that comes from arrayOfObjects but here is where I can’t see how could I loop that array of objects and put the correct value. The only problem with that approach is that the result array will have some 0 values that come from the initiation array that I’m using, it would be better to me to only put the objects that actually have values and not 0 (I was thinking on another function to delete those keys with value = 0…)

How could I achieve it in a better way?

Fiddle:

https://jsfiddle.net/pmiranda/Lpscz6vt/

>Solution :

When iterating over an object, use findIndex on the headers to identify which index in the headers array the property being iterated over should go into. Create an object there if it doesn’t exist yet, and set the property.

const arrayOfObjects = [
  { A: 1, B: 2, C:3 },
  { A: 3, B: 4, C:1 }
];
const headers = [
  ['A', 'B'],
  ['C']
];

const toResultItem = (object) => {
  const resultItem = [];
  for (const [key, value] of Object.entries(object)) {
    const headersIndex = headers.findIndex(arr => arr.includes(key));
    resultItem[headersIndex] ??= {};
    resultItem[headersIndex][key] = value;
  }
  return resultItem;
};
console.log(arrayOfObjects.map(toResultItem));