How to merge objects from two arrays

Question

I have two arrays of objects

    let current = [
        {
            categoryId: 18,
            id: 'fire_18',
            test: 'test'
        }, {
            oldItem: "items that dont exist in new array should be deleted"
        }
    ]

    let new_data = [
        {
            id: 'fire_18',
            categoryId: 18,
            test1: 'test1',
        }, {
            newItem: "new items should be added to final"
        }
    ]

I need to merge those so the result is not missing data from current array. The desired result looks like this

    [
        {
            id: 'fire_18',
            categoryId: 18,
            test1: 'test1',
            test: 'test'
        }, {
            newItem: "new items should be added to final"
        }
    ]

Here is my attempt

let current = [
    {
        categoryId: 18,
        id: 'fire_18',
        test: 'test'
    }, {
        oldItem: "items that dont exist in new array should be deleted"
    }
]

let new_data = [
    {
        id: 'fire_18',
        categoryId: 18,
        test1: 'test1',
    }, {
        newItem: "new items should be added to final"
    }
]

console.log(' === Current ==>', current);
console.log(' === New ==>', new_data);

new_data.map(newItem => {
    let currentMatch;
    try { // incase new item newItem.categoryId wont exist
        currentMatch = current.find(c => c.categoryId == newItem.categoryId) || {};
    } catch (error) { // in that case, no need to merge
        currentMatch = {};
    }
    return Object.assign(currentMatch, newItem);
});
console.log(' === Merged ==>', new_data);

the main thing wrong still is test key from the current arr is missing after merge.

Can anyone modify the pen to not delete keys from the current arr?

I've gone ahead and edited your question to include your attempt as a snippet in the question itself, as opposed to an external link. In the future, please make sure all necessary code is in the question itself. Users shouldn't have to visit a second website to see the complete question :) — Tyler Roper
– Tyler Roper, Commented Sep 19, 2019 at 19:39
Where did name and slugName come from in your expected results? — Maria
– Maria, Commented Sep 19, 2019 at 19:43
@Maria it was old irrelevant data from a prev version. I edited my question to reflect more accurately. — Omar
– Omar, Commented Sep 19, 2019 at 19:45
Please refer to this stackoverflow.com/questions/19480008/… — Milind Agrawal
– Milind Agrawal, Commented Sep 19, 2019 at 19:48

Charlie · Accepted Answer · 2019-09-19 19:57:28Z

1

Note that Array.map method returns a new array. You are not logging this merged new array - but one of your old arrays.

Also, you don't need try catch here. You may also note that if the categoryId is undefined, the objects will still match. So, you need a check for that.

let current = [
    {
        categoryId: 18,
        id: 'fire_18',
        test: 'test'
    }, {
        oldItem: "items that dont exist in new array should be deleted"
    }
]

let new_data = [
    {
        id: 'fire_18',
        categoryId: 18,
        test1: 'test1',
    }, {
        newItem: "new items should be added to final"
    }
]



newArray = new_data.map(newItem => {
    let currentMatch;
        
        
     currentMatch = current.find(c => c.categoryId === newItem.categoryId && newItem.categoryId) || {};
  
  
    return Object.assign(currentMatch, newItem);
});
console.log(' === Merged ==>', newArray);

edited Sep 19, 2019 at 19:57

answered Sep 19, 2019 at 19:48

Charlie

24k12 gold badges65 silver badges96 bronze badges

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

Comments

Sagar Chaudhary · Accepted Answer · 2019-09-19 19:48:31Z

0

You can use lodash for this.

finalArr = _(_.flatten([current, new_data]))
                                        .groupBy('id')
                                        .map(_.spread(_.assign))
                                        .value();

answered Sep 19, 2019 at 19:48

Sagar Chaudhary

1,40310 silver badges24 bronze badges

Comments

ray · Accepted Answer · 2019-09-19 19:51:33Z

0

Like this? I'm not sure what you're expecting to happen with the newItem and oldItem entries.

let current = [{
  categoryId: 18,
  id: 'fire_18',
  test: 'test'
}]

let new_data = [{
  id: 'fire_18',
  categoryId: 18,
  test1: 'test1',
}]

const result = Object.values([...current, ...new_data].reduce((acc, {
  categoryId,
  ...other
}) => ({
  ...acc,
  [categoryId]: {
    categoryId,
    ...other
  }
}), {}));

console.log(result);

answered Sep 19, 2019 at 19:51

ray

27.3k5 gold badges31 silver badges30 bronze badges

Comments

Milind Agrawal · Accepted Answer · 2019-09-19 19:54:07Z

0

You can use es6 spread operator to meet your requirement

  var current = [{
    categoryId: 18,
    id: 'fire_18',
    name: 'Servers',
    slugName: 'fire_18',
    test: 'test'
}]

var new_data = [{
    id: 'fire_18',
    categoryId: 18,
    name: 'Servers',
    slugName: 'fire_18'
}]

const results = new_data.map(item => {
    let newItem = { ...item };
    const currentMatchItem = current.find(c => c.categoryId == newItem.categoryId);

    if (currentMatchItem) {
        newItem = { ...currentMatchItem, ...newItem };
    }

    return newItem;
});

console.log(results);

answered Sep 19, 2019 at 19:54

Milind Agrawal

2,9541 gold badge15 silver badges22 bronze badges

Comments

A. Meshu · Accepted Answer · 2019-09-19 19:54:41Z

0

I found this. On your code it goes like that:

let current = [
    {
        categoryId: 18,
        id: 'fire_18',
        test: 'test'
    }, {
        oldItem: "items that dont exist in new array should be deleted"
    }
]

let new_data = [
    {
        id: 'fire_18',
        categoryId: 18,
        test1: 'test1',
    }, {
        newItem: "new items should be added to final"
    }
]

function merge(a, b, prop){
  var reduced = a.filter(function(aitem){
      return ! b.find(function(bitem){
          return aitem[prop] === bitem[prop];
      });
  });
  return reduced.concat(b);
}
console.log(merge(current, new_data, "id") );

answered Sep 19, 2019 at 19:54

A. Meshu

4,1782 gold badges24 silver badges35 bronze badges

2 Comments

Omar Over a year ago

this is great. but test is missing from current[0] in the merged results

A. Meshu Over a year ago

Well @Charlie's solutions much more modern anyways (:

Collectives™ on Stack Overflow

How to merge objects from two arrays

5 Answers 5

Comments

Comments

Comments

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

Comments

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related