How does one create an object based on the precedence of another object's key order?

Question

I have an object like this -

const obj = {
    'veh1': 'Car',
    'veh2': 'Bicycle',
    'veh3': 'Truck',
    'wheels1': '4',
    'wheels2': '2',
    'wheels3': '8'
}

I want an object which have entries mapped like- veh1 to wheels1 , veh2 to wheels2 , veh3 to wheels3 and so on The resultant object should be like this-

const result = {
    'Car': '4',
    'Bicycle': '2',
    'Truck': '8'
}

I know, we can do it directly like this -

{
   [obj.veh1]: obj.wheels1,
   [obj.veh2]: obj.wheels2,
   [obj.veh3]: obj.wheels3
}

But what will be the better way? The number of entries can be any number 'n'.

How can I attain this through javascript?

Answer 1

You can do something like this:

const vehicles = {};
const wheels = {};
const result = {};

for (key in obj) {
  if (key.startsWith("veh")) {
    const id = key.replace("veh", "");
    vehicles[id] = obj[key];
    if (wheels.hasOwnProperty(id)) {
      result[vehicles[id]] = wheels[id];
    }
  } else if (key.startsWith("wheels")) {
    const id = key.replace("wheels", "");
    wheels[id] = obj[key];
    if (vehicles.hasOwnProperty(id)) {
      result[vehicles[id]] = wheels[id];
    }
  }
}

Answer 2

1. Create entries (key value pairs) from the provided object.
2. Sort the entries by each of an entry's key.
3. Finally create a new objects from the upper (or left) as well the lower (or right) half of the before sorted entries.

 function localeCompare(a, b) { return (a.localeCompare && b.localeCompare && a.localeCompare(b)) || (((a < b) && -1) || ((a > b) && 1) || 0); } function compareEntriesByKey(entryA, entryB) { return localeCompare(entryA[0], entryB[0]); } function createKeyValuePairFromSortedEntryHalfs(obj, $, idx, entries) { if (((idx + 1) % 2) === 0) { const keyIdx = ((idx - 1) / 2); const valueIdx = (keyIdx + Math.floor(entries.length / 2)); const key = entries[keyIdx][1]; const value = entries[valueIdx][1]; obj[key] = value; } return obj; } const obj = { 'wheels3': '8', 'veh3': 'Truck', 'wheels1': '4', 'veh1': 'Car', 'wheels2': '2', 'veh2': 'Bicycle', } const result = Object // (1) create entries (key value pairs) from the provided object. .entries(obj) // (2) sort the entries by each of an entry's key. .sort(compareEntriesByKey) // (3) finally create a new objects from the upper (or left) as // well the lower (or right) half of the before sorted entries. .reduce(createKeyValuePairFromSortedEntryHalfs, {}); console.log('result :', result); console.log('obj', obj); console.log( 'Object.entries(obj).sort(compareEntriesByKey)', Object.entries(obj).sort(compareEntriesByKey) ); console.log( 'proof of being a generic approach...', ` Object.entries({ 'foo-biz': 'biz', 'x': 111, 'foo-baz': 'baz', 'y': 222, 'foo-bar': 'bar', 'z': 333, }).sort( compareEntriesByKey ).reduce( createKeyValuePairFromSortedEntryHalfs, {} ) =>`, Object.entries({ 'foo-biz': 'biz', 'x': 111, 'foo-baz': 'baz', 'y': 222, 'foo-bar': 'bar', 'z': 333, }).sort( compareEntriesByKey ).reduce( createKeyValuePairFromSortedEntryHalfs, {} ) );

 .as-console-wrapper { min-height: 100%!important; top: 0; }

Answer 3

const obj = {
  'veh1': 'Car',
  'veh2': 'Bicycle',
  'veh3': 'Truck',
  'wheels1': '4',
  'wheels2': '2',
  'wheels3': '8'
}

let res = {};
let keys = Object.keys(obj);
let i;
for(i = 0; i < keys.length; i ++) {
  if(keys[i].slice(0, 3) === 'veh') {
    res[obj[keys[i]]] = obj[`wheels${keys[i].slice(3)}`];
  }
}

console.log(res);