Add property from one array into another array with the same key

Question

Instead of explaining the problem in words, I've just made a quick visual representation below.

Say I have the following array:

let arr1 = [
  {
    id: 1,
    someKey: someValue
  },
  {
    id: 2,
    someKey: someValue
  },
]

and another array:

let arr2 = [
  {
    id: 1,
    numberOfItems: 10
  },
  {
    id: 2,
    numberOfItems: 20
  },
]

How would I create the following array?

let result = [
  {
    id: 1,
    someKey: someValue,
    numberOfItems: 10
  },
  {
    id: 2,
    someKey: someValue,
    numberOfItems: 10
  },
]

So as you can see, both arrays have the same id value. I want to take numberOfItems: 10 from the second array and place it into the first array under the same id.

Note: the two ids are completely different, have different properties and length. The only similarity is the id

Do both arrays have the same length? The same content? And the same item order? — Joseph
– Joseph, Commented Oct 5, 2018 at 15:32

slider · Accepted Answer · 2018-10-05 15:40:46Z

4

You could first create a map with id as key and then combine the objects This would solve the problem in O(n):

let arr1 = [
  {
    id: 1,
    someKey: 3
  },
  {
    id: 2,
    someKey: 6
  },
];

let arr2 = [
  {
    id: 1,
    numberOfItems: 10
  },
  {
    id: 2,
    numberOfItems: 20
  },
];

let arr2Map = arr2.reduce((acc, curr) => {
  acc[curr.id] = curr
  return acc;
}, {});
let combined = arr1.map(d => Object.assign(d, arr2Map[d.id]));
console.log(combined);

answered Oct 5, 2018 at 15:40

slider

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Comments

Mohammed Ashfaq · Accepted Answer · 2018-10-05 16:07:54Z

0

let arr1 = [
  {
    id: 1,
    someKey: 3
  },
  {
    id: 2,
    someKey: 6
  },
];

let arr2 = [
  {
    id: 1,
    numberOfItems: 10
  },
  {
    id: 2,
    numberOfItems: 20
  },
];

let idToNumberOfItem = {};
arr2.forEach(({id, numberOfItems})=> idToNumberOfItem[id]=numberOfItems)

arr1.forEach((item)=> item['numberOfItems'] =  idToNumberOfItem[item.id])

console.log(arr1);

answered Oct 5, 2018 at 16:07

Mohammed Ashfaq

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