Calculate average from data in array of object and store in specific key from object

Question

Suppose I have an array of object,

const book = [{'name':'alpha','readingTime':1231},{'name':'alpha','readingTime':1254}, 
              {'name':'beta','readingTime':190},
              {'name':'theta','readingTime':909},{'name':'theta','readingTime':10}]

I want to calculate average for each name, such that expected O/P is

**{alpha:1242.5, beta:190, theta:459.5}**

For this I tried as ,

let calculatedValue = book.reduce((acc,curr) => acc+curr.readingTime,0)/book.length

This gives me average for all the object.

I'm unable to form logic corresponding to it.

Any guidance would really be helpful. If anyone needs any further information please let me know.

Nina Scholz · Accepted Answer · 2021-04-21 07:48:40Z

2

You could group by name and get the count and total of readingTime and build a new object with the averages.

const
    books = [{ name: 'alpha', readingTime: 1231 }, {  name: 'alpha', readingTime: 1254 }, { name: 'beta', readingTime: 190 }, { name: 'theta', readingTime: 909 }, { name: 'theta', readingTime: 10 }],
    averages = Object.fromEntries(
        Object.entries(books.reduce((r, { name, readingTime }) => {
            r[name] = r[name] || { count: 0, total: 0 };
            r[name].count++;
            r[name].total += readingTime;
            return r;
        }, {}))
        .map(([k, { count, total }]) => [k, total / count])
    );

console.log(averages);

edited Apr 21, 2021 at 7:48

answered Apr 21, 2021 at 7:36

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Siva Pradhan Over a year ago

Double question mark is giving me unexpected token, while using in vscode. What could be alternative for this

Nina Scholz Over a year ago

take a logical OR instead. please see edit.

Anil · Accepted Answer · 2021-04-21 07:57:05Z

Need more optimization (Fell free to edit ) but it works

const book = [{'name':'alpha','readingTime':1231},{'name':'alpha','readingTime':1254}, 
              {'name':'beta','readingTime':190},
              {'name':'theta','readingTime':909},{'name':'theta','readingTime':10}]


function avgReading(arr){
let alpha = { lengtharr : 0 ,readingAll : 0 };
let beta = {...alpha};
let theta = {...alpha};
arr.forEach((item) => {
  if(item.name === 'alpha') 
    alpha.lengtharr++;
    alpha.readingAll = alpha.readingAll + item.readingTime;
  if(item.name === 'beta') 
    beta.lengtharr++;
    beta.readingAll = beta.readingAll + item.readingTime;
 if(item.name === 'theta')
    theta.lengtharr++;
    theta.readingAll = theta.readingAll + item.readingTime;
});
const obj = {
'alpha' : alpha.readingAll /alpha.lengtharr,
'beta' : beta.readingAll /beta.lengtharr,
'theta' : theta.readingAll /theta.lengtharr
}
return obj;
}
console.log(avgReading(book))

Yadab · Accepted Answer · 2021-04-21 07:58:31Z

1

Here is another simple solution for you.

const book = [{'name':'alpha','readingTime':1231},{'name':'alpha','readingTime':1254}, 
{'name':'beta','readingTime':190},
{'name':'theta','readingTime':909},
{'name':'theta','readingTime':10}]

const result = {};

Object.values(book.reduce((acc, current) => {
    acc[current.name] = acc[current.name] || { count: 0, total: 0 };
    acc[current.name].total += current.readingTime;
    acc[current.name].count += 1;
    acc[current.name].name = current.name;

    return acc;
}, {})).forEach(({ name, count, total }) => { result[name] = total / count; });

console.log(result)

edited Apr 21, 2021 at 7:58

answered Apr 21, 2021 at 7:51

Yadab

1,9031 gold badge12 silver badges16 bronze badges

Comments

Saravanan · Accepted Answer · 2021-04-21 07:56:07Z

0

Tyy this

let obj = book.reduce((acc,curr) => {
    acc[curr['name']] = acc[curr['name']]?acc[curr['name']]:[0,0]
    acc[curr['name']][0]+=curr['readingTime'];
    acc[curr['name']][1]+=1;
    return acc;
}, {})

let calculatedValue ={};
Object.keys(obj).forEach(key=>calculatedValue[key]=obj[key][0]/obj[key][1])

edited Apr 21, 2021 at 7:56

answered Apr 21, 2021 at 7:35

Saravanan

8299 silver badges16 bronze badges

1 Comment

Wimanicesir Over a year ago

A switch case with always the same code, just different keys... You can program everything with a switch case but It's not maintainable..

Collectives™ on Stack Overflow

Calculate average from data in array of object and store in specific key from object

4 Answers 4

2 Comments

Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related