Javascript: how to avoid nested foreach in this case?

Question

to all! I have the following data:

const datas = [
  {
    first: 'id',
    secondLevel: [
      {
        second: 'id2',
        thirdLevel: ['a', 'b', 'c']
      },
      ...
    ]
    ...
  }
  ...
]

My goal is to create all possible associations with the data of the 3 levels

for example

[
  { 
    first: 'id', 
    second: 'id2', 
    third: 'a' 
  },
  { 
    first: 'id', 
    second: 'id2', 
    third: 'b' 
  },
  ...
]

I'm currently doing it with a foreach in a foreach in a foreach and it's horrible I'm sure I can do it really better.

Somebody can help me ? Thanks !

@Teemu, it looks more like a cartesian product of nested parts than jist a question of iterating objects. — Nina Scholz, Apr 14 '21 at 07:07
@NinaScholz you should reopen the question. The tagged answer link hasn't a fitting answer to this question. Also, if possible, please answer it. Because even I've been searching for the right answer to this question for some time now and haven't found it. — Tom Bombadil, Apr 14 '21 at 07:45

score 1 · Answer 1 · answered Apr 14 '21 at 08:32

You could take a recursive approach and get first the value part and the array. Then iterate the array and get either a value or object from the array for flattaning.

Finally add the value part the the rest and get a flat array of objects.

This approach works for unknow depth. Mabe a good idea is to omit a key name with a Level suffix, which would omit slicing.

const
    flat = object => {
        let value, array;
        Object.entries(object).forEach(([k, v]) => {
            if (Array.isArray(v)) array = { k: k.slice(0, -5), v };
            else value = { [k]: v };
        });
        return array.v.flatMap(o => o && typeof o === 'object'
            ? flat(o).flatMap(q => ({ ...value, ...q }))
            : { ...value, [array.k]: o }
        );

    },
    data = [{ first: 'id', secondLevel: [{ second: 'id2', thirdLevel: ['a', 'b', 'c'] }] }],
    result = data.flatMap(flat);

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Thank you Nina. Your answer was very helpful. And I learned a lot of new things from it. I did not even know that there was an array method called `flatMap`. lol — Tom Bombadil, Apr 14 '21 at 18:19

Javascript: how to avoid nested foreach in this case?

1 Answers1