Convert an array of objects into a nested object in JavaScript

Question

I have a JavaScript array of objects, like this:

var start = [{
  name: 'example name',
  nextItem: {}
},
{
  name: 'example name 2',
  nextItem: {}
},
{
  name: 'example name 3',
  nextItem: {}
}];

I want to convert this array into a single nested object, where the inner nextItem object of the first array item contains the whole object of the next array item. For example:

var output = {
  name: 'example name',
  nextItem: {
    name: 'example name 2',
    nextItem: {
      name: 'example name 3',
      nextItem: {}
    }
  }
}

Any ideas?

Have you already tried something, and do you stuck somewhere? — webdeb
– webdeb, Commented Aug 16, 2017 at 10:33
I'm voting to close this question as off-topic because the question shows input and expected output format but does not show any sign of effort. This is a requirement and not a problem statement. — Rajesh Dixit
– Rajesh Dixit, Commented Aug 16, 2017 at 10:40
@Rajesh - This question is perfectly valid. You only need to show attempted code if you're asking what is wrong with it. This is both a specific programming problem and a practical, answerable problem that is unique to software development. See here... stackoverflow.com/help/on-topic — Reinstate Monica Cellio
– Reinstate Monica Cellio, Commented Aug 16, 2017 at 10:49
@Rejesh if SO were so strict, 80% of questions would be closed. We should push on the OP like I did im my first comment, but close because the guy don't know where to start is a bit extreme — webdeb
– webdeb, Commented Aug 16, 2017 at 10:54
@Rajesh - please read the link I gave you. It explains why this question is perfectly valid. — Reinstate Monica Cellio
– Reinstate Monica Cellio, Commented Aug 16, 2017 at 12:46

webdeb · Accepted Answer · 2017-08-16 11:06:42Z

2

Could be done with a recursive function:

function nestItems(items) {
  var currentItem = items[0];
  if (!currentItem) return {};

  return {
     name: currentItem.name,
     nextItem: nestItems(items.slice(1))
  };
}


nestItems(start);

edited Aug 16, 2017 at 11:06

answered Aug 16, 2017 at 10:41

webdeb

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1 Comment

Rajesh Dixit Over a year ago

Should we really answer such question that do not show any sign of effort?

Yosvel Quintero · Accepted Answer · 2017-08-17 08:52:55Z

2

You can use Array.prototype.reduceRight().

Code:

var start = [{name: 'example name',nextItem: {}},{name: 'example name 2',nextItem: {}},{name: 'example name 3',nextItem: {}}],
    output  = start.reduceRight(function (a, c) {
      return {
        name: c.name, 
        nextItem: a
      }; 
    });

console.log(output );

Updated based on comment from @NinaScholz

edited Aug 17, 2017 at 8:52

answered Aug 16, 2017 at 10:56

Yosvel Quintero

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4 Comments

Nina Scholz Over a year ago

hm reverse? really? why not use reduceRight?

webdeb Over a year ago

Code is first place for humans, so readability is on 1st place

webdeb Over a year ago

Yeah, its not fair ik, the solution it self is ok, so upvote

Yosvel Quintero Over a year ago

I am totally agree that code should be in first place for humans. I have edited to make it more readable and better indented.. Thank you for your comments

vinoth h · Accepted Answer · 2017-08-16 10:41:40Z

0

Try this :

var start = [{
  name: 'example name',
  nextItem: {}
},
{
  name: 'example name 2',
  nextItem: {}
},
{
  name: 'example name 3',
  nextItem: {}
}];

function concat(start) {
    var output = start[0];
    temp = output;
    for(i = 1;i < start.length;i ++) {
        temp.nextItem = start[i];
        temp = temp.nextItem;
    }
    return output;
}

console.log(concat(start));

answered Aug 16, 2017 at 10:41

vinoth h

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Comments

Reinstate Monica Cellio · Accepted Answer · 2017-08-16 10:42:23Z

0

There may be a more graceful way of doing it, but this will do the trick. (The trick being to start at the bottom and work your way up).

var start = [{
  name: 'example name',
  nextItem: {}
},
{
  name: 'example name 2',
  nextItem: {}
},
{
  name: 'example name 3',
  nextItem: {}
}];

var output = {};

for (var i = start.length; i > 0; i--) {
  output = { name: start[i - 1].name, nextItem: output };
}

console.log(output);

answered Aug 16, 2017 at 10:42

Reinstate Monica Cellio

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2 Comments

Rajesh Dixit Over a year ago

Should we really answer such question that do not show any sign of effort?

Reinstate Monica Cellio Over a year ago

@Rajesh - The question is perfectly valid.

Steffen Schmitz · Accepted Answer · 2017-08-16 10:57:34Z

0

You can use reduce on the array to add the objects:

function appendRec(obj, newObj) {
    if (obj || obj.nextItem === {}) obj.nextItem = newObj
    else appendRec(obj.nextItem, newObj)
    return obj
}

var output = start.reduce((acc, obj) => {
    return appendRec(acc, obj)
}, { nextItem: { } }).nextItem;

edited Aug 16, 2017 at 10:57

answered Aug 16, 2017 at 10:34

Steffen Schmitz

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3 Comments

webdeb Over a year ago

This will produce a single object with a single nextItem, which is the last one in the list..

Steffen Schmitz Over a year ago

Correct, please prefer Yosvel Quinteros answer.

webdeb Over a year ago

I would prefer mine, is most elegant IMO :D

Nina Scholz · Accepted Answer · 2017-08-16 11:47:27Z

You could use and take the returned accumulator as target for the nested object without mutating the original array.

var start = [{ name: 'example name', nextItem: {} }, { name: 'example name 2', nextItem: {} }, { name: 'example name 3', nextItem: {} }],
    result = {};

start.reduce(function (o, a) {
    o.name = a.name;
    o.nextItem = {};
    return o.nextItem;
}, result);

console.log(result);
console.log(start);

ES6 with mutating the original array.

var start = [{ name: 'example name', nextItem: {} }, { name: 'example name 2', nextItem: {} }, { name: 'example name 3', nextItem: {} }],
    result = {};

start.reduce(function (o, a) {
    Object.assign(o, a);
    return o.nextItem;
}, result);

console.log(result);
console.log(start);

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