Order by nested object property inside a array

Question

I'm stuck on this one thing trying to take top 3 manufacturers by numberOfCars, and, to do the same with cars: [], take top 3 by numberoOfCars

audi: {
  cars: [], 
  collectionName: '',
  numberOfCars: 0
}

I can do the first level with lodash like

_.take(_.orderBy(modelData, 'numberoOfCars', 'desc'), 3)

but I'm lost on doing the same on cars array as mentioned.

const mock = []

for (let i = 0; i < 140; i++) {
  let manufacturerName
  let name

  if (i < 20) {
    manufacturerName = 'Audi'
    name = 'A6'
  } else if (i > 19 && i < 40) {
    manufacturerName = 'BMW'
    name = '420 GC'
  } else if (i > 19 && i < 40) {
    manufacturerName = 'Mercedes'
    name = 'AMG'
  } else if (i > 39 && i < 60) {
    manufacturerName = 'Mazda'
    name = '6'
  } else if (i > 59 && i < 80) {
    manufacturerName = 'Volvo'
    name = 'V90'
  } else if (i > 79 && i < 100) {
    manufacturerName = 'Renault'
    name = 'Model'
  } else if (i > 99 && i < 120) {
    manufacturerName = 'Lamborghini'
    name = 'Aventador'
  } else if (i > 119 && i < 140) {
    manufacturerName = 'Volkswagen'
    name = 'Golf'
  }

  mock.push({
    id: i,
    name: name,
    displayName: 'display-name ' + Math.floor(Math.random() * 10),
    manufacturer: manufacturerName,
    numberoOfCars: Math.floor(Math.random() * 100000),
  })
}

const dataModel = mock.reduce((accumulator, currentValue) => {
  const key = currentValue.manufacturer

  if (accumulator[key] === undefined) {
    accumulator[key] = {
      collectionName: '',
      numberoOfCars: 0,
      cars: []
    }
  }

  if (accumulator[key].collectionName === '') {
    accumulator[key].collectionName = currentValue.manufacturer
  }

  if (currentValue.numberoOfCars !== undefined) {
    accumulator[key].numberoOfCars += currentValue.numberoOfCars
  }

  if (currentValue.numberoOfCars !== undefined) {
    accumulator[key].cars.push({
      name: currentValue.name,
      numberOfCars: currentValue.numberoOfCars
    })
  }

  return accumulator
}, {})

console.log(dataModel)

score 0 · Answer 1 · answered Oct 28 '19 at 20:36

I guess it should be something like this:

const cars = Object.keys(dataModel).reduce((acc, item) => {
  const collection = dataModel[item]
  return acc.concat(collection.cars)
}, []);

const top3cars = _.take(_.orderBy(cars, 'numberOfCars', 'desc'), 3);

score 0 · Accepted Answer · answered Oct 28 '19 at 20:48

Iterate over the keys in the outer object, order those keys by the number of cars associated with that key in the outer then pick the first 3 keys.

Then, reduce each key into an object that clones the value associated with that key and orders the cars in that value and takes the first 3:

var filtered = _.chain(dataModel)
    .keys()
    .orderBy(k=>dataModel[k].numberOfCars, 'desc')
    .take(3)
    .reduce((coll,k)=>{
        coll[k] = _.clone(dataModel[k]);
        coll[k].cars = _.chain(coll[k].cars)
            .orderBy('numberOfCars', 'desc')
            .take(3)
            .value();
        return coll;
    }, {})
    .value();

Example on jsfiddle

Credit to this answer by VLAZ for help on how to filter an object's items by an ordering over its values.

Thanks. I'm trying to understand one thing, is there a way to do this without the second reduce, like why is that necessary? Dont take it the wrong way, this is my learning process :) — Dejan.S, Oct 30 '19 at 06:56

Order by nested object property inside a array

2 Answers2