How to create Object with nested Objects from an Array

Question

I have an array [1, 2, 3] and I want to transfer it to object with nested parent-child objects's series like this :

{ value: 1, rest: { value: 2, rest: { value: 3, rest: null } }

If I have an array [1, 2, 3, 4] the result will be like this :

{ value: 1, rest: { value: 2, rest: { value: 3, rest: { value:4, rest:null } }

The best effort of me is this snippet of code :

const arrayToList = (array) => {
  let list = { value: null, rest: null };
  for (let e of array) {
    array.indexOf(e) === 0 && (list.value = e);
    array.indexOf(e) >= 1 && (list.rest = { value: e });
  }
  return list;
};
console.log(arrayToList([1, 2, 3]));

did you see my answer ? if there's something went wrong with it please let me know — Boussadjra Brahim
– Boussadjra Brahim, Commented Aug 14, 2020 at 20:14

ibrahim mahrir · Accepted Answer · 2020-06-20 01:43:02Z

8

You can use reduceRight like so:

let obj = arr.reduceRight((rest, value) => ({ value, rest }), null);

It starts building the object from the inside out; it starts by creating the innermost object and then it uses that object as the rest property for the next outer object and so on until there are no more items in the array.

Demo:

let obj = [1, 2, 3, 4].reduceRight((rest, value) => ({ value, rest }), null);

console.log(obj);

edited Jun 20, 2020 at 1:43

answered Jun 20, 2020 at 0:18

ibrahim mahrir

31.8k5 gold badges50 silver badges78 bronze badges

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

3 Comments

Ala Eddine Menai Over a year ago

I'd just say: Wonderful! because I hate writing functions with if-else.

ibrahim mahrir Over a year ago

@MenaiAlaEddine-Aladdin Thanks! The trick here is to start from the last item of the array and building the object from the inside out. Even if you use a simple for loop instead of reduceRight, if you start from the last item, you won't need if-else.

ibrahim mahrir Over a year ago

@MenaiAlaEddine-Aladdin ... like this jsfiddle.net/gd94npqf which is pretty much exactly what reduceRight is doing

mickl · Accepted Answer · 2020-06-20 00:13:30Z

1

You can create such object by running below recursive function:

let arr = [1, 2, 3, 4];

let transform = (arr, obj) => {
   if(arr.length === 0){
      return obj;
   } else {
      let last = arr[arr.length - 1];
      let newArr = arr.slice(0, arr.length - 1);
      
      return transform(newArr, { value: last, rest: obj || null })
   }
};

console.log(transform(arr));

answered Jun 20, 2020 at 0:13

mickl

50.1k9 gold badges71 silver badges99 bronze badges

1 Comment

Ala Eddine Menai Over a year ago

I want to avoid recursive functions for long-time execution if the array will be big.

Kalimah · Accepted Answer · 2020-06-20 00:16:11Z

1

Use a recursive function:

let array = [1, 2, 3];

function arrayToL(array) {
  let el = array.splice(0, 1)[0];
  let rtn = {
    value: el
  }

  rtn.rest = (array.length > 0) ? arrayToL(array) : null;

  return rtn;
}

console.log(arrayToL(array));

answered Jun 20, 2020 at 0:16

Kalimah

11.5k11 gold badges48 silver badges86 bronze badges

Comments

Boussadjra Brahim · Accepted Answer · 2020-07-05 17:54:34Z

1

I suggest another solution using the spread operator and reversing the array and start building object from the array end :

let arr = [1, 2, 4, 5]

let obj = {} //object to be built

arr.slice().reverse().forEach(item => { //i used the slice method 
  //in order to avoid mutating
  //the original variable
  obj = { ...obj,
    ...{
      value: item,
      rest: obj
    }
  };

})

console.log(obj)

answered Jul 5, 2020 at 17:54

Boussadjra Brahim

90k19 gold badges163 silver badges183 bronze badges

Collectives™ on Stack Overflow

How to create Object with nested Objects from an Array

4 Answers 4

3 Comments

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related