Convert JS Array to a nested Object

Question

What is the best way to convert:

['[Title A]','child A','child B', '[Title B]', 'child C', 'child D']

to:

{
  0: {
      'title': 'Title A',
      'children': ['child A', 'child B']
     }
  1: {
       'title': 'Title B',
       'children': ['Child C', 'Child D']
     }
}

I have this so far which checks on the presence of brackets [] and I tried to add this to an object with a dynamic index which increments during a for loop every time a title with brackets is found:

let index = 0;
let listObject = {};
for (const listItem of listItems) {
   const titleValue = listItem.match(/\[(.*?)\]/);
   if (titleValue) {
     ++index;
     listObject[index].title = titleValue[1];
   } else {
     listObject[index].children = [listItem];
   }
}

console.log(listObject);

Why is the result an object with "numierc" properties with objects and not an array of objects? — Andreas
– Andreas, Commented Nov 24, 2020 at 16:52

Yasmin · Accepted Answer · 2020-11-24 20:15:43Z

1

For the sake of simplicity let's first make an array of objects:

const res = arr.reduce((acc, cur) => {
  const titleValue = cur.match(/\[(.*?)\]/)
  titleValue ?
    acc.push({
      title: cur,
      children: []
    }) :
    acc[acc.length - 1].children.push(cur)

  return acc
}, [])

Now you can use the spread operator to have the nested object:

{...res}

answered Nov 24, 2020 at 20:15

Yasmin

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Sunil Kumar · Accepted Answer · 2020-11-24 18:06:39Z

0

const array = ['[Title A]','child A','child B', '[Title B]', 'child C', 'child D'];

let objToPush = {};
let objToSend = {};
array.map((d) => {
 if (/^\[[^\]]+\]$/.test(d)) {
  if (Object.keys(objToPush).length > 0) {
     objToSend[Object.keys(objToSend).length] = { ...objToPush };
     objToPush = {};
  }
  objToPush.title = d.substring(1, d.length - 1);
 } else {
  objToPush.children = objToPush.children ? [...objToPush.children, d] : [d]
 }
});
objToSend[Object.keys(objToSend).length] = { ...objToPush };
console.log('objToPush', objToSend);

it worked for me (JSFiddle https://jsfiddle.net/wepbzdfL/48/)

edited Nov 24, 2020 at 18:06

answered Nov 24, 2020 at 18:01

Sunil Kumar

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Comments

Marius · Accepted Answer · 2020-11-24 17:28:49Z

Just updated yours so the logic is sound. Can see what you tried.

Read up on creating new objects and arrays in JS, and when you can add to them.

let listItems = ['[Title A]', 'child A', 'child B', '[Title B]', 'child C', 'child D'];

let index = 0;
var listObject = {};
for (const listItem of listItems) {
  const isTitle = listItem[0] == "[" && listItem[listItem.length - 1] == "]"
  if (isTitle) {
    ++index;
    listObject[index] = {
      title: listItem.substring(1, listItem.length -1),
      children: [] //Create Array
    }; //Create Object
  } else {
    listObject[index].children.push(listItem); //Add to children array
  }
}

console.log(listObject);

To add on why I used an index lookup, instead of regex,

Run this:

var testArray = [];

var arrayCount = 20000000;

var regexMatch = /\[(.*?)\]/;

for (var i = 0; i < arrayCount; i++) {
  testArray.push("[" + makeid(Math.round(Math.random() * 10)) + "]")
}

console.log(testArray.length);
var start = new Date();
console.log(start.toString());

for (var i = 0; i < arrayCount; i++) {
  var testItem = testArray[i];
  if (testItem.match(regexMatch)) {

  } else {

  }
}

console.log("regex took " + (new Date().getTime() - start.getTime()) / 1000 + " seconds");

start = new Date();
for (var i = 0; i < arrayCount; i++) {
  var testItem = testArray[i];
  if (testItem[0] === "[" && testItem[testItem.length - 1] === "]") {

  } else {

  }
}

console.log("index lookup took " + (new Date().getTime() - start.getTime()) / 1000 + " seconds");

function makeid(length) {
  var result = '';
  var characters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
  var charactersLength = characters.length;
  for (var i = 0; i < length; i++) {
    result += characters.charAt(Math.floor(Math.random() * charactersLength));
  }
  return result;
}

Valentin Briand · Accepted Answer · 2020-11-24 17:43:43Z

0

I don't know if it's the "best" way, but this is my solution:

const array = [
  "[Title A]",
  "child A",
  "child B",
  "[Title B]",
  "child C",
  "child D"
];

let index = -1;
const res = array.reduce((acc, curr) => {
  if (/^\[[^\]]+\]$/.test(curr)) {
    acc = {
      ...acc,
      [++index]: { title: curr.substring(1, curr.length - 1), children: [] }
    };
  } else {
    acc[index].children = [...acc[index].children, curr];
  }
  return acc;
}, {});

console.log(res);

edited Nov 24, 2020 at 17:43

answered Nov 24, 2020 at 17:03

Valentin Briand

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