Generated recursive object based on array

Question

I have an array, which is a list of keys: ['one', 'two', 'three'].

I need to generate an object, of the following format:

{
  path: 'one',
  nested: {
    path: 'two',
    nested: {
      path: 'three'
    }
  }
}

So far I've tried a couple of approaches, but they seem quite messy (I have one method which uses while(current = array.pop()) but it requires several conditionals to handle the first and last elements.

Is there a neater recursive strategy?

@Barmar I haven't found any answer that solves the problem recursively in both places, and I have purely recursive solution to share, please reopen this questionç — Bakhtiiar Muzakparov, Jul 05 '17 at 16:55
What is the expected result when the array is empty? Yes, your current structure does indeed require special handling of the last element, it would be better if it had something like `nested: null`. — Bergi, Jul 05 '17 at 17:07
@Bergi we would just add extra condition that checks for that and returns immediately empty object https://jsfiddle.net/6rpg5jc1/ — Bakhtiiar Muzakparov, Jul 05 '17 at 17:11
@BakhtiiarMuzakparov I'm suggesting *not* to return an empty object for that case. Exactly to avoid extra conditions. — Bergi, Jul 05 '17 at 17:13
@BakhtiiarMuzakparov I would return `null` or `undefined` - or maybe even a special object - that would also be the `nested` value of the last path segment. — Bergi, Jul 05 '17 at 17:20
@BakhtiiarMuzakparov No I'm not. I was asking the OP whether it is ok or not. — Bergi, Jul 05 '17 at 17:24

Nenad Vracar · Accepted Answer · 2017-07-05T16:53:48.950

6

You can use reduce() method and as accumulator pass object that you want add properties to.

var arr = ['one', 'two', 'three']
var obj = {}

arr.reduce(function(r, e, i) {
  r.path = e;
  return arr[i+1] ? r.nested = {} : r
}, obj)

console.log(obj)

If you want to use just recursion without loop you can create function like this.

var data = ['one', 'two', 'three']
var obj = {}

function makeObj(arr, n, o) {
  if (n == arr.length - 1) o.path = arr[n]
  else {
    o.path = arr[n];
    o.nested = {}
    makeObj(arr, n += 1, o.nested)
  }
  return o.nested
}

makeObj(data, 0, obj)
console.log(obj)

edited Jul 05 '17 at 16:53

answered Jul 05 '17 at 16:20

Nenad Vracar

118,580
15
151
176

Mutating the accumulator is absolutely ugly. Why not just use `reduceRight` instead? – Bergi Jul 05 '17 at 17:09

Thomas · Answer 2 · 2017-07-05T16:46:16.410

2

var arr = ['one', 'two', 'three'];
var tree = arr.reduceRight((nested, path) => {
  return nested? {path, nested}: {path};
}, null);

console.log(tree);

or even better/simpler, just:

var arr = ['one', 'two', 'three'];
var tree = arr.reduceRight((nested, path) => ({path, nested}), null);

console.log(tree);

It simplifies things for the JS engine if all objects have the same hidden class (simplified: same property names).

edited Jul 05 '17 at 16:46

answered Jul 05 '17 at 16:39

Thomas

11,958
1
14
23

`reduceRight` is the only correct appraoch here. +1! – Bergi Jul 05 '17 at 17:08
The engine optimisation isn't really relevant. It mostly simplifies things in the code and for the programmer! – Bergi Jul 05 '17 at 17:12

Angels · Answer 3 · 2017-07-05T16:33:33.807

0

let arr = ['one', 'two', 'three'], obj = {};

obj['path'] = arr[arr.length - 1];
for(let i = arr.length - 2; i >= 0; i--) {
  obj = {
    path: arr[i],
    nested: obj
  };
}
console.log(obj);

edited Jul 05 '17 at 16:33

answered Jul 05 '17 at 16:23

Angels

230
1
8

it doesn't look recursive to me – Bakhtiiar Muzakparov Jul 05 '17 at 16:23
Recursive solution will fail if array will contain too many elements. But if author needs only recursive solution, so be it ;) – Angels Jul 05 '17 at 16:27
How will a recursive solution fail? – War10ck Jul 05 '17 at 16:28

score 0 · Answer 4 · answered Jul 05 '17 at 16:24

You can use a decrementing for loop to solve this problem:

var props = ['one','two','three'],
    obj;
    
for(var a = props.length;a--;) {
    var temp = { path: props[a] };
    if(obj) {
        temp.nested = obj;
    }
    obj = temp;
}

console.log(obj);

Generated recursive object based on array

4 Answers4