Create array of objects based on two another arrays of objects

Question

I went through SO to find the sulution but I failed...

I have two arrays of objects and I want to create the third one based on them and add some new keys/values.

Base Data

const oldArray = [
{id: 1, name: 'Test', age: 25, skill: 120}, 
{id: 2, name: 'Test25', age: 10, skill: 120}];

Data with some modifications

const newArray = [
{id: 1, name: 'Test2', age: 50, skill: 200},
{id: 2, name: 'Test25', age: 25, skill: 120}];

I would like to receive something like:

const expectedResultArray = [
  {id: 1, oldName: 'Test', newName: 'Test2', oldAge: 25, newAge: 50, ageDifference: 25, oldSkill: 120, newSkill: 200, skillDifference: 80 },
  {id: 2, oldName: 'Test25', newName:'Test25', oldAge: 10, newAge: 25, ageDifference: 15, oldSkill:120, newSkill: 120, skillDefference: 0}]

As You can see, the expected array is a combination of old and totally new calculations based on the two arrays. How can i achieve that ? I tried with reduce() however i got stuck trying:

var createNewArray = (...objects) => 
  Object.values(objects.reduce((a, e) => {
    a[e.id] = a[e.id] || {id: e.id};
  // struggling to proceed here 

    return a;
  }, {}))
;

console.log(createNewArr(...oldArray, ...newArray));

I'm not following how your oldArray and newArray should result in your expectedResultArray, based on your code. The IDs and old/new names between the old and new arrays don't correspond. In any case, I'd do a straightfoward for-loop over the longer array (if one is longer) and go from there. — mykaf
– mykaf, Commented Nov 23, 2020 at 17:08
This is the data from 2 tables. Data from one table is a baseData. On the second table (second array) user is able to perform some modifications. The third array of objects (the expected one) is the combination of those arrays. That's why You see oldName and newName there :) — AdamKniec
– AdamKniec, Commented Nov 23, 2020 at 17:13
what is the purpose of this line: a[e.id] = a[e.id] || {id: e.id}? And how are you pairing items between the arrays? — mykaf
– mykaf, Commented Nov 23, 2020 at 17:37
I made a small edit. I gave the wrong id's to the objects. Well the whole idea is that I want to create a new array where some of the data comes from the oldArray: oldAge, some from the mofified array - newAge and eg ageDifference should be the result of substraction. newAge - oldAge — AdamKniec
– AdamKniec, Commented Nov 23, 2020 at 17:42
I'd loop through one array, find the matching id in the second array, then do calculations from there. I would start with a straightforward for-loop, then move on to reduce() once you've got your algorithm down. — mykaf
– mykaf, Commented Nov 23, 2020 at 17:48

Girish Sasidharan · Accepted Answer · 2020-11-23 18:23:23Z

1

If the objects are in the same order then you can try this. Otherwise we need to find the element based on the id.

const oldArray = [
{id: 1, name: 'Test', age: 25, skill: 120}, 
{id: 2, name: 'Test25', age: 10, skill: 120}];

const newArray = [
{id: 1, name: 'Test2', age: 50, skill: 200},
{id: 2, name: 'Test25', age: 25, skill: 120}];

const Result = newArray.map((item, i) => {
  let oldConverted = renameObject(oldArray[i], 'old');
  let newConverted = renameObject(item, 'new');
  newConverted.ageDifference = newConverted.newAge - oldConverted.oldAge;
  newConverted.skillDefference = newConverted.newSkill - oldConverted.oldSkill;
  return Object.assign({}, newConverted, oldConverted);
});

function renameObject(obj, type) {
  let newObj = {};
  newObj.id = obj.id;
  Object.keys(obj).forEach((key) => {
    if (key != 'id') {
      newObj[type + capitalize(key)] = obj[key];
    }
  });
  return newObj;
}

function capitalize(string) {
  return string.charAt(0).toUpperCase() + string.slice(1);
}
console.log(Result);

answered Nov 23, 2020 at 18:23

Girish Sasidharan

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1 Comment

AdamKniec Over a year ago

Thanks, however I found a really simple solution. I posted a comment below. I guess I was too tired and did not see a simple way ;) Thx for help anyway

AdamKniec · Accepted Answer · 2020-11-24 21:50:40Z

0

Well, the solution was easier than I expected... (Facepalm)

const oldArray = [{id: 1, name: 'Test', age: 25, skill: 120},  {id: 2, name: 'Test25', age: 10, skill: 120}];

const newArray = [{id: 1, name: 'Test2', age: 50, skill: 200}, {id: 2, name: 'Test25', age: 25, skill: 120}];


const generateNewArr = () => {
 return oldArray.map((row,index) => {
   return {
     id: row.id,
     oldName: row.name,
     newName: newArray[index].name,
     oldAge: row.age,
     newAge: newArray[index].age,
     ageDifference: newArray[index].age - row.age,
     oldSkill: row.skill,
     newSkill: newArray[index].skill,
     skillDifference: newArray[index].skill - row.skill
   }
 })
}

  
console.log(generateNewArr())

answered Nov 24, 2020 at 21:50

AdamKniec

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