CODEWITHSUNDEEP
javascriptangular
Mariem
Mariem

Reputation: 133

How to reduce table of objects and calculate the sum of similar values?

I'm creating a function in angular and I want to reduce a list of objects like this example :

var tab =[{name:'i', value:13}, {name:'j', value:10},{name:'i', value:8}]

I want to get this result :

tab = [{name:'i', value:21},{name:'j', value:10}]

Upvotes: 0

Views: 301

Answers (3)

Micah
Micah

Reputation: 691

If you are just chopping off the last element within an array you should be able to just use the reduceRight() function. Click here for more on the reduce Method 

let tab =[{name:'i', value:13}, {name:'j', value:10},{name:'k', value:8}]

tab.reduceRight();

console.log(tab);

Upvotes: 1

Spectric
Spectric

Reputation: 31990

You can check whether the array contains an object with the same name property with Array.find, and if so, increment the value property. Otherwise, push to the array.

var tab = [{name: 'i', value: 13}, {name: 'j', value: 10}, {name: 'i', value: 8}]
const result = tab.reduce((a, b) => {
  let found = a.find(e => e.name == b.name);
  return found ? found.value += b.value : a.push(b), a
}, [])

console.log(result);

Upvotes: 2

Lukasz Gawrys
Lukasz Gawrys

Reputation: 1334

The answer provided by Spectric is a default solution for this problem and would be preferred in most cases as it is clear and straightforward. However I asked myself if we can solve it without additional iteration (via find function) and came up with following solution.

var tab = [{ name: 'i', value: 13 }, { name: 'j', value: 10 }, { name: 'i', value: 8 }, { name: 'j', value: 8 }];
const result = tab.reduce((a, b, i) => {
    let found = a.tmp.hasOwnProperty(b.name);
    return !found ? a.res[a.tmp[b.name] = i] = b : a.res[a.tmp[b.name]].value += b.value, a;
}, { tmp: {}, res: [] }).res;

console.log(result);

It is adding auxiliary tmp object saving index of a given unique element in the result array and allows us to do everything in one iteration. I could imagine this to be better in terms of performance if we had a lot of objects of only few distinct types.

Upvotes: 1

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