Javascript array of objects group and sum items

Question

I'm struggling with getting the desired output of Array of objects. So let's I have this Array of object:

var cars = [
    { make: 'audi', model: 'r8', quantity: '5' }, 
    { make: 'audi', model: 'rs5', quantity: '10'}, 
    { make: 'ford', model: 'mustang', quantity: '3' }, 
    { make: 'kia', model: 'optima', quantity: '9' },
    { make: 'audi', model: 'rw7', quantity: '2' },
    { make: 'ford', model: 'fusion', quantity: '7' }
],

The desired Output:

var cars = [
    { make: 'audi', sumQuantity: '17' }, 
    { make: 'ford', sumQuantity: '10' }, 
    { make: 'kia',  sumQuantity: '9' }
],

I tried to map through them but didn't solve my problem, hope you guys help out here! Thanks.

Jakub Kylián · Accepted Answer · 2020-11-29 10:53:01Z

3

This works fine

Object.values(
  cars.reduce((agg, car) => {
    if (agg[car.make] === undefined) agg[car.make] = { make: car.make, sumQuantity: 0 }
    agg[car.make].sumQuantity += +car.quantity
    return agg
  }, {})
)

answered Nov 29, 2020 at 10:53

Jakub Kylián

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Comments

The Otterlord · Accepted Answer · 2020-11-29 10:39:14Z

1

Probably not the most concise solution as I'm no JavaScript master.

First we get all the cars added up in a slightly easier to handle format. Then we rebuild it into the format requested above.

var newCars = [];
var makes = {};

for (var i=0; i<cars.length; i++) {
    var car = cars[i];
    var keys = Object.keys(makes)
    if (keys.includes(car.make)) {
        makes[car.make] += parseInt(car.quantity)
    } else {
        makes[car.make] = parseInt(car.quantity)
    }
}

var keys = Object.keys(makes)

for (var i=0; i<keys.length; i++) {
    newCars.push({make: keys[i], sumQuantity: makes[keys[i]]})
}

answered Nov 29, 2020 at 10:39

The Otterlord

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Comments

Vaibhav · Accepted Answer · 2020-11-29 10:39:32Z

0

You could do something like this

function desiredOutput(cars) {
  var output = []

  for (let i = 0 ; i < cars.length ; i++) {
    output.push({"make": cars[i].make, "sumQuantity": "Value based on your logic."});
  }

  return output 
}

var cars = [
    { make: 'audi', model: 'r8', quantity: '5' }, 
    { make: 'audi', model: 'rs5', quantity: '10'}, 
    { make: 'ford', model: 'mustang', quantity: '3' }, 
    { make: 'kia', model: 'optima', quantity: '9' },
    { make: 'audi', model: 'rw7', quantity: '2' },
    { make: 'ford', model: 'fusion', quantity: '7' },
]

let output = desiredOutput(cars);

answered Nov 29, 2020 at 10:39

Vaibhav

6126 silver badges14 bronze badges

2 Comments

The Otterlord Over a year ago

I can't quite see how this is meant to work. By pushing before all objects containing the same make are combined, you are essentially recreating the same list again, value for value. Even if the OP has some "logic" (not mentioned in the post), the output would still be invalid.

Vaibhav Over a year ago

The logic could be inserted within the for loop to get the desired values for the key "sumQuantity". It's not quite clear from the post how the rest of the things are going on. Considering that the array of objects was just supposed to be converted into a different array of objects with some different keys, this solution will work. I did try this solution before posting it and it did give me the output in the form suggested by the post.

Rodrigo Rodrigues · Accepted Answer · 2022-09-27 19:39:57Z

I was looking for a quick, almost "one-liner" answer in this thread, provided that this is a trivial but common exercise.

I couldn't find any for my like. The other answers are fine but I am not much into boilerplate.

So, let me add one, then:

obj = cars.reduce((c,{make:m,quantity:q})=>({...c,[m]:(c[m]||0)+Number(q)}),{})
output = Object.entries(obj).map(([m,q])=>({make:m,sumQuantity:q.toString()}))

var cars = [
    { make: 'audi', model: 'r8', quantity: '5' }, 
    { make: 'audi', model: 'rs5', quantity: '10'}, 
    { make: 'ford', model: 'mustang', quantity: '3' }, 
    { make: 'kia', model: 'optima', quantity: '9' },
    { make: 'audi', model: 'rw7', quantity: '2' },
    { make: 'ford', model: 'fusion', quantity: '7' }
]

obj = cars.reduce((c,{make:m,quantity:q})=>({...c,[m]:(c[m]||0)+Number(q)}),{})
output = Object.entries(obj).map(([m,q])=>({make:m,sumQuantity:q.toString()}))

console.log(output)

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