Javascript object reorganization with performance

Question

I am working on a problem where I have to group an array of objects from one form into another.

An example is better than 1000 words:

var initialData = [
  {
    house: { id: 1, text: "white" },
    room: { id: 1, text: "red" },
    price: 2.1
  },
  {
    house: { id: 1, text: "white" },
    room: { id: 2, text: "blue" },
    price: 3.1
  },
  {
    house: { id: 1, text: "white" },
    room: { id: 3, text: "red" },
    price: 5.8
  },
  {
    house: { id: 2, text: "black" },
    room: { id: 1, text: "yellow" },
    price: 9.1
  },
  {
    house: { id: 2, text: "black" },
    room: { id: 2, text: "green" },
    price: 7.7
  },
];

And the new object should look like this:

var finalObject = {
  houses: [
    {
      id: 1, text: "white",
      rooms: [
        { id: 1, text: "red", price: "2.1" },
        { id: 2, text: "blue", price: "3.1" },
        { id: 3, text: "red", price: "5.8" }
      ]
    },
    {
      id: 2, text: "black",
      rooms: [
        { id: 1, text: "yellow", price: "9.1" },
        { id: 2, text: "green", price: "7.7" }
      ]
    }
  ]
};

I have to find unique houses with all their rooms and also to add each price from initial object inside room.

I'm wondering which would be the best way to do this since I will have a huge amount of elements?

I have some ideas with multiple loops, but to me it seems a bit too complex my solution.

Update: my question is not the same as the one candidate for duplication because I don't use lodash, and my object has to be refactored a bit, not just regrouped.

Possible solution (inspired by @Gael's answer)

finalObject = {}

for (var i = 0; i < initialData.length; ++i) {
  var item = initialData[i];
  var id = item.house.id;
  if(!finalObject[id]) {
    finalObject[id] = item.house;
    finalObject[id].rooms = [];
  }
  var room = item.room;
  room.price = item.price;

  finalObject[id].rooms.push(room);
}

console.log(finalObject);

It looks like you would only need one loop. You could go through each element and add it to a new array, grouping it based on the house, then rooms, then id. — victor, Jun 23 '17 at 20:15
You should post those ideas and what you've written so far to solve the problem. — chazsolo, Jun 23 '17 at 20:19
Possible duplicate of [How to group array of objects by key](https://stackoverflow.com/questions/40774697/how-to-group-array-of-objects-by-key) — Heretic Monkey, Jun 23 '17 at 20:32

Ori Drori · Accepted Answer · 2017-06-23T21:02:43.703

Use Array#reduce with a helper object:

var initialData = [{"house":{"id":1,"text":"white"},"room":{"id":1,"text":"red"},"price":2.1},{"house":{"id":1,"text":"white"},"room":{"id":2,"text":"blue"},"price":3.1},{"house":{"id":1,"text":"white"},"room":{"id":3,"text":"red"},"price":5.8},{"house":{"id":2,"text":"black"},"room":{"id":1,"text":"yellow"},"price":9.1},{"house":{"id":2,"text":"black"},"room":{"id":2,"text":"green"},"price":7.7}];

var dict = {}; // helper object
var result = initialData.reduce(function(houses, obj) { // reduce the data
  var house = dict[obj.house.id]; // get the house from the dict by id
  
  if(!house) { // if house wasn't found
    house = Object.assign({}, obj.house, { rooms: [] }); // create a new house object
    houses.push(house); // push it into the array of houses
    dict[house.id] = house; // add it to the dict by id
  }
  
  house.rooms.push(obj.room); // push the room to the current house
  
  return houses;
}, []);

console.log(result);

You can also achieve it using ES6 Map and spread syntax:

const initialData = [{"house":{"id":1,"text":"white"},"room":{"id":1,"text":"red"},"price":2.1},{"house":{"id":1,"text":"white"},"room":{"id":2,"text":"blue"},"price":3.1},{"house":{"id":1,"text":"white"},"room":{"id":3,"text":"red"},"price":5.8},{"house":{"id":2,"text":"black"},"room":{"id":1,"text":"yellow"},"price":9.1},{"house":{"id":2,"text":"black"},"room":{"id":2,"text":"green"},"price":7.7}];

const result = [...initialData.reduce((houses, { house, room }) => { // reduce the data to a Map
  const currentHouse = houses.get(house.id) || Object.assign({}, house, { rooms: [] }); // get the current house from the map by id, or create a new one
  
  currentHouse.rooms.push(room); // push the room to the current house
  
  return houses.set(currentHouse.id, currentHouse); // set the house to the map, and return it
}, new Map()).values()]; // get the values of the map and spread to an array

console.log(result);

score 2 · Answer 2 · answered Jun 23 '17 at 20:33

2

You should use a map:

var myMap = new Map();

var keyObj = {}, // ideally your room object with id


// setting the values
myMap.set(keyString, "value associated with 'a string'"); // not recommended for your case

Or:

myMap.set(keyObj, 'value associated with keyObj'); // should be rooms

myMap.size; // the number of items you added

answered Jun 23 '17 at 20:33

Pritam Banerjee

17,953
10
93
108

this is just a different data structure, but what is the strategy to group in the way I need? – V. Sambor Jun 23 '17 at 20:42
1

@V.Sambor make objects of a house class key and rooms array containing room objects it's value. – Pritam Banerjee Jun 23 '17 at 20:44
1

Thank you for your help, I'm going to try this, be right back! :) – V. Sambor Jun 23 '17 at 20:53

kamoroso94 · Answer 3 · 2017-06-23T21:19:23.613

Depending on if you want to preserve the initial data or not will affect the solution. I've assumed you want to keep the original object and produce a new one.

You can do this in a single loop if you use a Map object to remember where existing houses are by there id property. If the house has already been inserted into the result, you just need to add the new room. Otherwise, you need to create a new house object and store it's index in the map.

function transformHouses(houses) {
  const houseMap = new Map();
  const result = {houses: []};

  for(const house of houses) {
    if(houseMap.has(house.id)) {
      const index = houseMap.get(house.id);
      const room = Object.assign({price: house.price}, house.room);

      result.houses[index].rooms.push(room);
    } else {
      const room = Object.assign({price: house.price}, house.room);
      const entry = Object.assign({rooms: [room]}, house.house)

      housesMap.set(house.id, result.houses.length);
      result.houses.push(entry);
    }
  }

  return result;
}

score 1 · Answer 4 · answered Jun 23 '17 at 21:02

var houses= {};

initialData.forEach(function(item){
  
  if( !houses[ item.house ] ){
  
    houses[ item.house ]= item.house;
    houses[ item.house ].rooms= {};
  }
  houses[ item.house ].rooms[ item.room.id ]= item.room;
  houses[ item.house ].rooms[ item.room.id ].price= item.price;
  
});

Javascript object reorganization with performance

4 Answers4