Calculate multiple sum of an array of objects in Javascript

Question

I am trying to compute multiple sums from an array of objects: [{value1: 3, value2:6}, {value1: 2, value2: 4},...]. Potentially, the object can contain an unspecified number of keys (i.e. value1:, value2:, value3:..., value n). Based on this example, the sum of all the value1 keys should return 5 while the sum of all the value2 keys should return 10.

What I did so far is as follows:

let sum = 0;
const myArrayObject = [{value1: 3, value2:6}, {value1: 2, value2: 4}];
const objectKeys = Object.keys(myArrayObject[0]); //Gives me the keys of the object

objectKeys.forEach(key => {
  myArrayObject.map((entry) => {
    sum += entry[key];
  });
});
return sum;

This however gives me the total 15. Is there a way to actually compute the sum for all the value1 keys and value2 keys separately?

Does this answer your question? Sum similar keys in an array of objects — GrafiCode
– GrafiCode, Commented Aug 26, 2021 at 16:30

Isaac · Accepted Answer · 2021-08-26 16:41:31Z

1

const myArrayObject = [{value1: 3, value2:6}, {value1: 2, value2: 4}];

const result = myArrayObject.reduce((accum, current) => {
  Object.entries(current).forEach(([key, value]) => {
    accum[key] = (accum[key] + value) || value;
  })
  return {
    ...accum
  }
}, {});

console.log(result)

Not as elegant as others but you may take a look, basically for each and every element, loop thru the entries and add it to a temporarily variable during reduce function

answered Aug 26, 2021 at 16:41

Isaac

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Comments

jarmod · Accepted Answer · 2021-08-26 16:36:52Z

1

Here's a simple reduce-based solution:

const values = [
  { value1: 3, value2: 6 },
  { value1: 2, value2: 4 },
];

const basket = values.reduce((basket, value) => {
  for (const [key, count] of Object.entries(value)) {
    if (!basket[key]) {
      basket[key] = 0;
    }

    basket[key] += count;
  }

  return basket;
}, {});

console.log(basket); // { value1: 5, value2: 10 }

answered Aug 26, 2021 at 16:36

jarmod

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2 Comments

James Over a year ago

This solution will work even with differing keys in each element of values.

jarmod Over a year ago

@James I think you're saying that if one, and only one, of the values includes value3, that value3 will (correctly) appear in the resulting basket. Yes, indeed.

ℛɑƒæĿᴿᴹᴿ · Accepted Answer · 2021-08-26 16:38:20Z

0

Example using an array myArraySum for store the sum results:

let sum = 0;
let myArraySum = []; 
const myArrayObject = [{value1: 3, value2:6}, {value1: 2, value2: 4}];
const objectKeys = Object.keys(myArrayObject[0]);

objectKeys.forEach(key => {
  sum = 0;
  myArrayObject.map((entry) => {
    sum += entry[key];
  });
   myArraySum.push(sum);
});

console.log(myArraySum);

answered Aug 26, 2021 at 16:38

ℛɑƒæĿᴿᴹᴿ

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Comments

0stone0 · Accepted Answer · 2021-08-26 16:42:05Z

0

If we use an extra object to 'group' those keys, we can later use that object to show the result:

const myArray = [{value1: 3, value2:6}, {value1: 2, value2: 4}];
let res = {};

for (let i = 0; i < myArray.length; i++) {
  for (const [key, value] of Object.entries(myArray[i])) {
    if (!res[key]) {
      res[key] = 0;
    }
    res[key] += value;
  }
}

for (const [key, value] of Object.entries(res)) {
  console.log(`${key} has the sum of ${value}`);
}

answered Aug 26, 2021 at 16:42

0stone0

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Comments

Nina Scholz · Accepted Answer · 2021-08-26 16:48:15Z

0

By having same keys, you could reduce the array and create a new object with sums.

const
    objects = [{ value1: 3, value2: 6 }, { value1: 2, value2: 4 }],
    result = objects.reduce((a, b) => Object.fromEntries(Object
        .entries(a)
        .map(([k, v]) => [k, v + b[k]])
    ));

console.log(result);

Approach for different keys.

const
    objects = [{ value0: 42, value1: 3, value2: 6 }, { value1: 2, value2: 4, value3: -42 }],
    result = objects.reduce((r, o) => Object
        .entries(o)
        .reduce((t, [k, v]) => (t[k] = (t[k] || 0) + v, t), r), 
    {});

console.log(result);

edited Aug 26, 2021 at 16:48

answered Aug 26, 2021 at 16:38

Nina Scholz

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Comments

Behemoth · Accepted Answer · 2021-08-26 16:54:18Z

0

Classic case for Array.prototype.reduce():

const data = [
  { value1: 3, value2: 6 },
  { value1: 2, value2: 4 },
];

const result = data.reduce((acc, curr) => {
  Object.entries(curr).forEach((e) => (acc[e[0]] += e[1]));
  return acc;
});

console.log(result);

edited Aug 26, 2021 at 16:54

answered Aug 26, 2021 at 16:47

Behemoth

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