Merge each JavaScript object in huge array with another object

Question

I have an array of JavaScript object which has over millions of objects, I want to merge each object in the array with a specific object with fixed key and values

[{prop1:"a",prop2:"b"}, {prop1:"c",prop2:"d"}] -- Array of object


{id:"1","dept":"Finance"} -- object to be merge in

Currently I am iterating over each object in array and adding the key and value one by one which is very time consuming.

I am looking for an alternate solution in JavaScript to merge two object like a bulk merge without iterating on each object to save CPU time.

How do you expect to be able to alter every object in the array without iterating over each one? You can't get more efficient than O(n) and it sounds like you've already tried that solution. — Elan Hamburger
– Elan Hamburger, Commented Dec 20, 2019 at 6:47
You could wrap the array with another object, implementing the api you need, that only merges the given objects on access. Sort of a lazy merge. Though feasibility it depends on how that outer containing array is passed around / used. — Yoshi
– Yoshi, Commented Dec 20, 2019 at 6:54
@ElanHamburger, I have no idea if that is possible, as in past I have done object key conversion to string using regular expression without iterating over each object. — Akshay Naik
– Akshay Naik, Commented Dec 20, 2019 at 6:59

Barmar · Accepted Answer · 2019-12-20 06:47:06Z

1

Use Object.assign() to merge objects.

array_of_objects.forEach(obj => Object.assign(obj, object_to_merge_in));

answered Dec 20, 2019 at 6:47

Barmar

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4 Comments

Akshay Naik Over a year ago

will it be faster than iterating on each object and adding the key value pairs individually ?

Barmar Over a year ago

I'd expect it to be, since it's highly optimized code in the JavaScript internals.

Yoshi Over a year ago

@RohanKumar I think a more realistic test is needed. jsben.ch/WZ2OV

Barmar Over a year ago

@RohanKumar On your test my version is fastest by 5%. But the main difference is the reduced memory, which is not apparent with only 2 elements in the array.

Moshi · Accepted Answer · 2019-12-20 06:58:59Z

0

At first for performance-wise, it is O(n) complexity. So there is no way out without doing a loop through each object whether you use Object.assign, array.map or any other method.

If you have so many json object manipulation related works in your project, life will be easier if you use lodash.

There are plenty of methods as your requirement in that library

    _.merge(object, [sources], [customizer], [thisArg])
    _.assign(object, [sources], [customizer], [thisArg])
    _.extend(object, [sources], [customizer], [thisArg])
    _.defaults(object, [sources])
    _.defaultsDeep(object, [sources])

answered Dec 20, 2019 at 6:58

Moshi

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Comments

Rohan Kumar · Accepted Answer · 2019-12-20 06:48:57Z

-1

You can use .map() without using of loop to merge a new object in array of objects

var objArr = [{prop1:"a",prop2:"b"}, {prop1:"c",prop2:"d"}],
    obj = {id:"1","dept":"Finance"} ;

var mapArr = objArr.map(x => Object.assign(x,obj));

console.log(mapArr);

answered Dec 20, 2019 at 6:48

Rohan Kumar

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8 Comments

Barmar Over a year ago

Why create a new list with map()? Object.assign() modifies the object in place.

Rohan Kumar Over a year ago

@Barmar Map is used to iterate an array internally, and Object.assign() is used to assign/copy an object from another. So we need to use map to iterate each object then copy a new Object to an existing one.

Barmar Over a year ago

Object.assign() modifies the first argument in place, it doesn't create a new object.

Barmar Over a year ago

You only get new objects if you write Object.assign({}, x, obj)

Barmar Over a year ago

With over a million objects in the array, creating new copies might be a memory issue.

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