How can I merge two arrays of objects in JavaScript

Question

I have a simple question. I have two arrays A and B, I want to retain A objects if B has the same ID. For example:

const A = [{id: "price", value: "1"}]

const B = [{id: "price", value: "0"}, {id: "number", value: "0"}]

Expected result:

[{id: "price", value: "1"}, {id: "number", value: "0"}}]

How can I do this?

I tried to map A and foreach B inside A but it didn't work.

Do you want to replace A's objects or B's objects? The expected result is confusing — ibrahim mahrir
– ibrahim mahrir, Commented May 9, 2019 at 1:24
The term is "merging" and has been covered plenty of times... — Heretic Monkey
– Heretic Monkey, Commented May 9, 2019 at 1:24
I have edit. Thats right, I want to merge these two arrays into one — Tiago Castro
– Tiago Castro, Commented May 9, 2019 at 1:25
If A and B have same ID, do you want to keep A or B? Your question does not match your expected result. — yqlim
– yqlim, Commented May 9, 2019 at 1:26
Possible duplicate of es6 merge two array of objects and override the existing object — Heretic Monkey
– Heretic Monkey, Commented May 9, 2019 at 1:27

ibrahim mahrir · Accepted Answer · 2019-05-09 01:39:21Z

8

const result = A.concat(B.filter(bo => A.every(ao => ao.id != bo.id)));

Concatenate all the objects from A with objects from B that aren't in A (which is done by filtering only objects from B where there isn't an object in A with the same id).

Example:

const A = [{id: "price", value: "1"}];

const B = [{id: "price", value: "0"}, {id: "number", value: "0"}];

const result = A.concat(B.filter(bo => A.every(ao => ao.id != bo.id)));

console.log(result);

edited May 9, 2019 at 1:39

answered May 9, 2019 at 1:33

ibrahim mahrir

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Comments

Jack Bashford · Accepted Answer · 2019-05-09 01:30:33Z

1

You'd use reduce on the merged array - also turn the value into a number:

const A = [{id: "price", value: "1"}];
const B = [{id: "price", value: "0"}, {id: "number", value: "0"}];
const res = Object.values([...A, ...B].reduce((acc, { id, value }) => {
  if (acc[id]) acc[id].value += parseInt(value);
  else acc[id] = { id, value: parseInt(value) };
  return acc;
}, {}));
console.log(res);

.as-console-wrapper { max-height: 100% !important; top: auto; }

answered May 9, 2019 at 1:30

Jack Bashford

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3 Comments

Tiago Castro Over a year ago

The problem is that my value is not always a number.

Jack Bashford Over a year ago

Well then what will your value be? A decimal?

Tiago Castro Over a year ago

It can be a number or a string. I want to replace

gp. · Accepted Answer · 2019-05-09 02:04:57Z

0

Another option that you could try (I believe it would be O(n) ) is to convert arrays to objects with id as key then extend (jquery.extend or pure js implementation) then convert the merged object back to array.

const A = [{id: "price", value: "1"}];

const B = [{id: "price", value: "0"}, {id: "number", value: "0"}];

//convert arrays to objects
var Bx = {};
B.forEach(i => Bx[i.id] = i);

var Ax = {};
A.forEach(i => Ax[i.id] = i);

//copy all matching id properties from A to B
A.forEach(i => Bx[i.id] = Ax[i.id]);

//convert the merged object to array
var C = [];
Object.getOwnPropertyNames(Bx).forEach(i => C.push(Bx[i]));

console.log(C);

edited May 9, 2019 at 2:04

answered May 9, 2019 at 1:57

gp.

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