Home creating an multidimensional Object dynamically from an multidimensional array

Questions

creating an multidimensional Object dynamically from an multidimensional array

November 24, 2021

Im trying to create an multidimensional Object like this one:

{ A : {a1: {},a2:{}}, B: {b1:{},b2:{}}}

from an multidimensional array like this one:

let array1 = [
      ['A', 'a1'],
      ['A', 'a1'],
      ['A', 'a2'],
      ['B', 'b1'],
      ['B', 'b1'],
      ['B', 'b2'],
    ];

I’m trying this for some hours now and was also reading plenty of entrys here on stackoverflow, but nothing really fits this specific case.

What i did so far:

    let array1 = [
      ['A', 'a1'],
      ['A', 'a1'],
      ['A', 'a2'],
      ['B', 'b1'],
      ['B', 'b1'],
      ['B', 'b2'],
    ];

    let object1 = {};

    array1.forEach(function (subArray) {
      let level1 = subArray[0];
      let level2 = subArray[1];

      object1[[level1]] = { ...{ [level2]: {} } };
    });

    console.log('object: ', object1);
    //desired output:  object = { A : {a1: {},a2:{}}, B: {b1:{},b2:{}}}
    //what I get:  object = { A : {a2:{}}, B: {b2:{}}}

So somehow in my code the entrys like {a1: {}} are getting overwritten in each iteration instead of adding a new entry.

Thanks a lot in advance.

>Solution :

Keep previous properties using ...object1[[level1]]:

    let array1 = [
      ['A', 'a1'],
      ['A', 'a1'],
      ['A', 'a2'],
      ['B', 'b1'],
      ['B', 'b1'],
      ['B', 'b2'],
    ];

    let object1 = {};

    array1.forEach(function (subArray) {
      let level1 = subArray[0];
      let level2 = subArray[1];

      object1[[level1]] = {
        ...object1[[level1]], // Keep previous properties
        ...{ [level2]: {} } // Add new
      };
    });

    console.log('object: ', object1);