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 — Heretic Monkey
– Heretic Monkey, Commented Mar 7, 2018 at 18:30

Hassan Imam · Accepted Answer · 2018-03-07 18:24:22Z

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 7, 2018 at 18:24

Hassan Imam

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1 Comment

JSess Over a year ago

Thank you for providing an explanation with yours, so I'll accept this answer.

Saikat Hajra · Accepted Answer · 2018-03-07 18:31:15Z

1

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

let me know if it works

answered Mar 7, 2018 at 18:31

Saikat Hajra

6803 silver badges12 bronze badges

1 Comment

JSess Over a year ago

This does work, but I have accepted the other answer already. I appreciate your help, Saikat Hajra.

th3n3wguy · Accepted Answer · 2018-03-07 21:06:05Z

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 7, 2018 at 21:06

answered Mar 7, 2018 at 18:24

th3n3wguy

3,7242 gold badges25 silver badges31 bronze badges

5 Comments

JSess Over a year ago

This doesn't appear to function. I've accepted another answer, so thank you for your help anyway th3n3wguy

th3n3wguy Over a year ago

@JSess => I updated the code because I was missing the external library and a closing bracket.

th3n3wguy Over a year ago

The main difference between my answer and your accepted answer is that mine is using Lodash, which is what you originally asked for. Lol.

JSess Over a year ago

I know, but I implemented his first and it worked. I can't accept multiple answers or I would. I upvoted you, though.

th3n3wguy Over a year ago

@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. :)

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