How to loop through two arrays and find common value object? Javascript using forEach

Question

I need to looping thought two arrays and find where is value expanded = true set to first array?

example of first array:

[ 
 { id: 1 , name: 'Test 1' , expended = false },
 { id: 2 , name: 'Test 2' , expended = false },
 { id: 3 , name: 'Test 3' , expended = false }
]

exaple of second array:

[ 
 { id: 1 , name: 'Test 1' , expended = false },
 { id: 2 , name: 'Test 2' , expended = true },
 { id: 3 , name: 'Test 3' , expended = false }
]

Different between two array is only expended value where is on second array is :

 { id: 2 , name: 'Test 2' , expended = true }

I need to loop thought first array and second and find in second array where is expended = true and just paste on first array.

The expected result above after the loop should be:

first array value

[ 
 { id: 1 , name: 'Test 1' , expended = false },
 { id: 2 , name: 'Test 2' , expended = true },
 { id: 3 , name: 'Test 3' , expended = false }
]

Please, I can't just copy the value of all array!

this example is not accepted:

this.secondArray = this.firstArray..

This is a simple example I sent you. I have 10 more parameters in the object that are changing, but it is only important for me to be expended to copy!

Literally, the value expended from the second array to copy to the first and that's it!

this.secondArray = this.firstArray.. wouldn't work anyway and this question is not a pleasant reading experience I feel like i'm being asked a question on an exam... — Jarne Kompier
– Jarne Kompier, Commented Oct 7, 2021 at 8:02
Does this answer your question? How to update one array with data from another array using Key of Id? also How can I update an array based on another array? and Update the first array object based on the second array — pilchard
– pilchard, Commented Oct 7, 2021 at 8:21

DecPK · Accepted Answer · 2021-10-07 08:50:42Z

2

You can achieve the result using Map and map

You can set the value of expended if value of expended of arr1 is false as

arr1.map((o) => ({ ...o, expended: o.expended || map.get(o.id).expended }))

const arr1 = [
  { id: 1, name: "Test 1", expended: false },
  { id: 2, name: "Test 2", expended: false },
  { id: 3, name: "Test 3", expended: false },
];

const arr2 = [
  { id: 1, name: "Test 1", expended: false },
  { id: 2, name: "Test 2", expended: true },
  { id: 3, name: "Test 3", expended: false },
];

const map = new Map(arr2.map((o) => [o.id, o]));

const result = arr1.map((o) => ({ ...o, expended: o.expended || map.get(o.id).expended }));
console.log(result);

/* This is not a part of answer. It is just to give the output fill height. So IGNORE IT */
.as-console-wrapper { max-height: 100% !important; top: 0; }

If you want the result with forEach

const arr1 = [
  { id: 1, name: "Test 1", expended: false },
  { id: 2, name: "Test 2", expended: false },
  { id: 3, name: "Test 3", expended: false },
];

const arr2 = [
  { id: 1, name: "Test 1", expended: false },
  { id: 2, name: "Test 2", expended: true },
  { id: 3, name: "Test 3", expended: false },
];

arr1.forEach((obj) => {
  const elementInArr2 = arr2.find((o) => o.id === obj.id);
  if (elementInArr2) obj.expended = obj.expended || elementInArr2.expended;
});

console.log(arr1);

/* This is not a part of answer. It is just to give the output fill height. So IGNORE IT */
.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Oct 7, 2021 at 8:50

answered Oct 7, 2021 at 8:07

DecPK

25.4k6 gold badges32 silver badges46 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

yajoj98337 Over a year ago

I need forEach friend..i need forEach... I'm using angular 9 and new Subject ... I can't do that. I intentionally wrote forEach

DecPK Over a year ago

@yajoj98337 code udpated with forEach also. This is even more simple than with Map

Majed Badawi · Accepted Answer · 2021-10-07 08:48:36Z

0

Using Array#reduce, iterate over the second array while updating a Map, if the object's expended is true, set the key to the id and the value to the object
Using Array#map, iterate over the first array. For every object check if the above map has its id and replace it, otherwise keep it

let 
  arr1 = [ { id: 1, name: 'Test 1', expended: false }, { id: 2, name: 'Test 2', expended: false }, { id: 3, name: 'Test 3', expended: false } ],
  arr2 = [ { id: 1, name: 'Test 1', expended: false }, { id: 2, name: 'Test 2', expended: true }, { id: 3, name: 'Test 3', expended: false } ];
  
const expenededMap = arr2.reduce((map, obj) => {
  if(obj.expended) map.set(obj.id, obj);
  return map;
}, new Map);

arr1 = arr1.map(obj => {
  if(obj.expended) return obj;
  const objFromArr2 = expenededMap.get(obj.id) || {};
  return objFromArr2.expended ? objFromArr2 : obj;
});

console.log(arr1);

Using just Array#forEach and Array#find:

let 
  arr1 = [ { id: 1, name: 'Test 1', expended: false }, { id: 2, name: 'Test 2', expended: false }, { id: 3, name: 'Test 3', expended: false } ],
  arr2 = [ { id: 1, name: 'Test 1', expended: false }, { id: 2, name: 'Test 2', expended: true }, { id: 3, name: 'Test 3', expended: false } ];
  
arr1.forEach((obj, i, arr) => {
  if(!obj.expended) {
    const objFromArr2 = arr2.find(({ id }) => id === obj.id) || {};
    if(objFromArr2.expended) arr[i] = objFromArr2;
  }
});

console.log(arr1);

edited Oct 7, 2021 at 8:48

answered Oct 7, 2021 at 8:06

Majed Badawi

28.5k4 gold badges30 silver badges56 bronze badges

2 Comments

yajoj98337 Over a year ago

I need forEach friend..i need forEach... I'm using angular 9 and new Subject ... I can't do that. I intentionally wrote forEach

Majed Badawi Over a year ago

@yajoj98337 you can only use forEach? can you use find with it for example?

Collectives™ on Stack Overflow

How to loop through two arrays and find common value object? Javascript using forEach

2 Answers 2

2 Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related