How to get the average from array of objects

Question

Below I reproduce my code for calculate average ratings for foods.

3+4+5+2 / 4 should be equal to 3.5. But this not gives me the correct output. What's wrong with my code?

const ratings = [
  {food:3},
  {food:4},
  {food:5},
  {food:2}
];

let food = 0;

ratings.forEach((obj,index)=>{
  food = (food + obj.food)/++index
})

console.log("FOOD",food)

Ankit Agarwal · Accepted Answer · 2018-09-26 08:34:23Z

4

Despite of having several answers I would like to add mine focusing to improve the code quality:

You can use destructuring in forEach() to just get the food property of the object as that is only the property you are interested with.
Despite of dividing inside loop we can have only one division operation after the loop is completed. This saves a lot of computation when the array is huge(thousands of objects)
You can use short hand like += in the loop for summing up the value.
You can make a single line code in forEach()

const ratings = [
  {food:3},
  {food:4},
  {food:5},
  {food:2}
];

let foodTotal = 0;
let length = ratings.length;
ratings.forEach(({food})=> foodTotal += food);

console.log("FOOD",foodTotal/length);

answered Sep 26, 2018 at 8:34

Ankit Agarwal

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3 Comments

Ankit Agarwal Over a year ago

@PathumSamararathna I will suggest to use this answer. Not because this is mine but this will help you code optimally.

margherita pizza Over a year ago

Sure!.even the first answer solved my problem. But this answer'll more help to the community.

Robby Cornelissen Over a year ago

In what sense does this answer improve code quality over simpler and more idiomatic answers like this one?

baao · Accepted Answer · 2018-09-26 08:25:40Z

2

You'd use reduce to sum, then simply divide by rating's length

const ratings = [
  {food:3},
  {food:4},
  {food:5},
  {food:2}
];

const avg = ratings.reduce((a, {food}) => a + food, 0) / ratings.length;
console.log(avg);

answered Sep 26, 2018 at 8:25

baao

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2 Comments

baao Over a year ago

You’re welcome. @PathumSamararathna You’ve accepted the wrong answer though. Even though it claims to be efficient and whatever, it isn’t. It introduces plenty of unneeded variables, uses forEach where reduce should be used, and so on.

Robby Cornelissen Over a year ago

This is indeed the most idiomatic JavaScript, and should be accepted in favor of any solution using forEach().

adam.k · Accepted Answer · 2018-09-26 08:33:00Z

2

Here is another solution using .reduce()

const ratings = [
  {food: 3},
  {food: 4},
  {food: 5},
  {food: 2}
]
const average = ratings.reduce((a, b) => {
  return {food: a.food + b.food}
}).food / ratings.length

console.log('FOOD', average)

answered Sep 26, 2018 at 8:33

adam.k

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Comments

vrintle · Accepted Answer · 2018-09-26 08:26:57Z

1

You need to divide by the number of elements after you have summed them together

const ratings = [
    {food:3},
    {food:4},
    {food:5},
    {food:2}
];

let food = 0;

ratings.forEach((obj,index)=>{
    food = (food + obj.food)
});

food = food / ratings.length;

console.log("FOOD",food)

edited Sep 26, 2018 at 8:26

vrintle

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answered Sep 26, 2018 at 8:24

Johan

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Comments

Ori Drori · Accepted Answer · 2018-09-26 08:28:24Z

1

You need to add the relative contribution to the average of each food.

Since average is - sum of items / number of items in your case it's

(3+4+5+2) / 4

Which we can split to

3/4 + 4/4 + 5/4 + 2/4

const ratings = [{"food":3},{"food":4},{"food":5},{"food":2}];

let food = 0;

ratings.forEach((obj) => {
  food = food + obj.food / ratings.length;
})

console.log("FOOD", food)

You can also use Array.reduce() to shorten the code a bit:

const ratings = [{"food":3},{"food":4},{"food":5},{"food":2}];

const food = ratings.reduce((r, { food }) => 
  r + food
, 0) / ratings.length;

console.log("FOOD", food)

edited Sep 26, 2018 at 8:28

answered Sep 26, 2018 at 8:21

Ori Drori

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Comments

Shababb Karim · Accepted Answer · 2018-09-26 09:07:29Z

0

What you are doing is 3/1 + 4/2 + 5/3 + 2/4 which is not equivalent to 3/4 + 4/4 + 5/4 + 2/4. What you can do is

ratings.forEach((obj,index)=>{
    food = (food + obj.food)
});

food = food / ratings.length;

console.log("FOOD",food)

If you are into functional way of doing things then I would use a reduce function to get the result.

const food = ratings.reduce((sum, { food }) => sum + food, 0) / ratings.length;

console.log("FOOD", food)

answered Sep 26, 2018 at 9:07

Shababb Karim

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