Merge nested array of objects by unique property and array

Question

I am finding a difficult time finding a solution for multiple levels of push / merging with Lodash and Underscore. Trying to avoid some messy nested loops with JS.

Here's an example of how I need to merge.

const arr = [
  {
    level : 'test',
    items : [1, 2, 3]
  },
  {
    level : 'tests',
    items : [1, 2, 3]
  }
];

const obj = {
  level : 'test',
  items : [4, 5, 6]
};


/* Output:
  [
    {
      level : 'test',
      items : [1, 2, 3, 4, 5, 6]
    },
    {
      level : 'tests',
      items : [1, 2, 3]
    }
  ];
*/

The obj level matches arr[0], and so the items array should merge. New, or unique levels should push to the array as a new object.

Is there a way I could achieve this through some combination of _.groupBy and _.mergeWith of Lodash? So far, I have gotten it to merge into a single array with two objects from the two respective unique levels, but when the items arrays merge it ends up with [4, 5, 6].

Any help would be appreciated.

Possible duplicate of [Merge javascript objects in array with same key](https://stackoverflow.com/questions/33850412/merge-javascript-objects-in-array-with-same-key) — Heretic Monkey, Mar 07 '18 at 18:30

score 2 · Accepted Answer · answered Mar 07 '18 at 18:24

2

You can use array#find to search for an object with same level value. Then, for a successful match array#concat items.

const arr = [ { level : 'test', items : [1, 2, 3] }, { level : 'tests', items : [1, 2, 3] } ]; 
const obj = { level : 'test', items : [4, 5, 6] };
const result = arr.find(o => o.level === obj.level);
if(result)
  result.items = result.items.concat(obj.items);
console.log(arr);

answered Mar 07 '18 at 18:24

Hassan Imam

21,956
5
41
51

Thank you for providing an explanation with yours, so I'll accept this answer. – JSess Mar 07 '18 at 19:32

th3n3wguy · Answer 2 · 2018-03-07T21:06:05.277

1

const arr = [
  {
    level : 'test',
    items : [1, 2, 3]
  },
  {
    level : 'tests',
    items : [1, 2, 3]
  }
];

const obj = {
  level : 'test',
  items : [4, 5, 6]
};


/* Output:
  [
    {
      level : 'test',
      items : [1, 2, 3, 4, 5, 6]
    },
    {
      level : 'tests',
      items : [1, 2, 3]
    }
  ];
*/

const newArr = _.map(arr, (val) => {
  return !_.isEqual(val.level, obj.level) ? val 
    : _.assign({}, val, {
      items: _.concat(val.items, obj.items)
    });
});

console.log(newArr);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.5/lodash.min.js"></script>

edited Mar 07 '18 at 21:06

answered Mar 07 '18 at 18:24

th3n3wguy

3,649
2
23
30

This doesn't appear to function. I've accepted another answer, so thank you for your help anyway th3n3wguy – JSess Mar 07 '18 at 19:35
@JSess => I updated the code because I was missing the external library and a closing bracket. – th3n3wguy Mar 07 '18 at 21:06
The main difference between my answer and your accepted answer is that mine is using Lodash, which is what you originally asked for. Lol. – th3n3wguy Mar 08 '18 at 23:50
I know, but I implemented his first and it worked. I can't accept multiple answers or I would. I upvoted you, though. – JSess Mar 09 '18 at 00:53
1

@JSess => That is fully-understandable. I should've made sure that my code was 100% functional first. Either way, I am glad that you found a working answer. :) – th3n3wguy Mar 09 '18 at 14:19

score 1 · Answer 3 · answered Mar 07 '18 at 18:31

1

arr.map((e)=>{e.level === obj.level && e.items.push(...obj.items);return e})

let me know if it works

answered Mar 07 '18 at 18:31

Saikat Hajra

670
3
12

2

This does work, but I have accepted the other answer already. I appreciate your help, Saikat Hajra. – JSess Mar 07 '18 at 19:35

Merge nested array of objects by unique property and array

3 Answers3