How to duplicate an object in an array by given quantity, ES6 and above

Question

I'm trying to convert an array of objects where i return duplicated objects if the object properties quantity is greater than 1.

const objects = [
  { id: 1, name: "Scissor", price: 2, quantity: 3 },
  { id: 2, name: "Hat", price: 6.5, quantity: 1 },
  { id: 3, name: "Socks", price: 0.5, quantity: 5 },
];


// desired return
[
  { id: 1, name: "Scissor", price: 2 }
  { id: 1, name: "Scissor", price: 2 }
  { id: 1, name: "Scissor", price: 2 }
  { id: 2, name: "Hat", price: 6.5}
  { id: 3, name: "Socks", price: 0.5 }
  { id: 3, name: "Socks", price: 0.5 }
  { id: 3, name: "Socks", price: 0.5 }
  { id: 3, name: "Socks", price: 0.5 }
  { id: 3, name: "Socks", price: 0.5 }
]

My code:

const objects = [
  { id: 1, name: "Scissor", price: 2, quantity: 3 },
  { id: 2, name: "Hat", price: 6.5, quantity: 1 },
  { id: 3, name: "Socks", price: 0.5, quantity: 5 },
];

let newObjects= [];

Object.entries(objects).forEach(([key, value]) => {

    for (let i=0; i < value.quantity; i++){
        newObjects.push({ id: value.id, name: value.name, price: value.price})
    }

});
console.log(newObjects);

So my code above does work, does return what i wanted, however i feel like there is a better/smoother and more of ES6 and beyond method. Could anyone please suggest a better way?

`Object.entries` already is ES6 and beyond. (Although it's absolutely unnecessary, since you never use the keys). — Bergi, Nov 15 '20 at 18:39
Combine any answer from [Create an array with same element repeated multiple times](https://stackoverflow.com/q/12503146/1048572) with a `flatMap` call and you're done. — Bergi, Nov 15 '20 at 18:43

Yousername · Accepted Answer · 2020-11-15T18:43:11.903

3

You could use .fill() and .flatMap().

const objects = [
  { id: 1, name: "Scissor", price: 2, quantity: 3 },
  { id: 2, name: "Hat", price: 6.5, quantity: 1 },
  { id: 3, name: "Socks", price: 0.5, quantity: 5 },
];
let newObjects = objects.flatMap(e=>
  Array(e.quantity).fill({id: e.id, name: e.name, price: e.price})
);
console.log(newObjects);

edited Nov 15 '20 at 18:43

answered Nov 15 '20 at 18:25

Yousername

1,012
5
15

1

Instead of `map`+`flat`, use `flatMap` – Bergi Nov 15 '20 at 18:40
Okay, I will use that instead. – Yousername Nov 15 '20 at 18:42

Guruparan Giritharan · Answer 2 · 2020-11-15T18:34:15.987

You can use an array reduce along with an array fill.

The map is required only if you want to have unique references otherwise you can fill using the same object.

const objects = [
  { id: 1, name: "Scissor", price: 2, quantity: 3 },
  { id: 2, name: "Hat", price: 6.5, quantity: 1 },
  { id: 3, name: "Socks", price: 0.5, quantity: 5 },
];

const output = objects.reduce((a, c) => {
  return a.concat(Array(c.quantity).fill({}).map(x=>({
    id: c.id,
    name: c.name,
    price: c.price
  })))
}, []);


console.log(output)

How to duplicate an object in an array by given quantity, ES6 and above

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