compare two array of objects with keys and if not found add it to the array

Question

array1 =  [
    {id: 1, height: 178}, {id: 1, height: 176},
    {id: 2, height: 168},{id: 2, height: 164}
]

array2 =  [
    {id: 1, height: ''},{id: 1, height: ''},
    {id: 2, height: ''},{id: 2, height: ''}, 
    {id: 3, height: ''}, {id: 3, height: ''}, 
    {id: 4, height: ''}, {id: 4, height: ''}
]

resultArray  = [
    {id: 1, height: 178},{id: 1, height: 176},
    {id: 2, height: 168},{id: 2, height: 164}, 
    {id: 3, height:''}, {id: 3, height: ''}, 
    {id: 4, height: ''}, {id: 4, height: ''}
]

I am looking to compare id of array1 with id of array2 and if any objects are missing in array1 then we add it to that array. Can you suggest me how to do it?

Thank you

Do you want to add them incrementally or all at once? I only ask because as soon as you add one, say `id: 3`, then `array1` will have that `id` in it so you wouldn't add more — Phil, Aug 13 '18 at 05:47
Possible duplicate of [Comparing two arrays of objects, and exclude the elements who match values into new array in JS](https://stackoverflow.com/q/32965688/9775003) — Sanoj_V, Aug 13 '18 at 05:48
All at once because i am going to map this resultArray to render the table. i am looking to get the result array with all the missing keys in array 2 even if they were duplicated. — CodingisLife, Aug 13 '18 at 05:50
https://stackoverflow.com/questions/19480008/javascript-merging-objects-by-id — gp., Aug 13 '18 at 05:55

score 2 · Accepted Answer · answered Aug 13 '18 at 05:53

2

I'd recommend using a set of array1's keys for fast lookup. Note that this mutates array1:

const array1 = [{id: 1, height: 178},{id: 1, height: 176},{id: 2, height: 168},{id: 2, height: 164}]
const array2 = [{id: 1, height: ''},{id: 1, height: ''},{id: 2, height: ''},{id: 2, height: ''}, {id: 3, height: ''}, {id: 3, height: ''}, {id: 4, height: ''}, {id: 4, height: ''}]

const ids = new Set(array1.map(e => e.id));

array2.forEach(e => {
  if (!ids.has(e.id)) {
    array1.push(e);
  }
});

console.log(array1);

answered Aug 13 '18 at 05:53

ggorlen

44,755
7
76
106

Nice! I had a feeling there'd be a nicer way to build the `Set` than using `reduce()` – Phil Aug 13 '18 at 05:55
Great!! This is what I am looking for. Works perfect for me. Thank you very much – CodingisLife Aug 13 '18 at 06:07

Saeed · Answer 2 · 2018-08-13T05:59:21.983

1-Save length of first array

2-Iterate through second array items

3-if the id does not exists or its index is bigger than length of array, push item to first array.

let array1 = [{ id: 1, height: 178 }, { id: 1, height: 176 }, { id: 2, height: 168 }, { id: 2, height: 164 }], array2 = [{ id: 1, height: '' }, { id: 1, height: '' }, { id: 2, height: '' }, { id: 2, height: '' }, { id: 3, height: '' }, { id: 3, height: '' }, { id: 4, height: '' }, { id: 4, height: '' }],
  arr1Length = array1.length;

array2.forEach(function(itm) {
  let index = array1.findIndex(function(it) {
    return it.id == itm.id;
  });
  if (-1 == index || arr1Length <= index) {
    array1.push(itm)
  }
});

console.log(array1)

Phil · Answer 3 · 2018-08-13T06:09:10.730

Create a Set of id properties from array1 using something like Array.prototype.reduce() or Array.prototype.map()
Filter out the entries from array2 that are not in the Set
Concatenate array1 with the filtered result

const array1 =  [{id: 1, height: 178},{id: 1, height: 176},{id: 2, height: 168},{id: 2, height: 164}]
const array2 =  [{id: 1, height: ''},{id: 1, height: ''},{id: 2, height: ''},{id: 2, height: ''}, {id: 3, height: ''}, {id: 3, height: ''}, {id: 4, height: ''}, {id: 4, height: ''}]

// Step #1
const knownIds = array1.reduce((set, {id}) => set.add(id), new Set())

// Steps 2 and 3
const resultArray = array1.concat(array2.filter(({id}) => !knownIds.has(id)))

console.info(resultArray)

compare two array of objects with keys and if not found add it to the array

3 Answers3