Get sum of property values within array of objects [duplicate]

Question

I am trying to get an object as output using JavaScript reduce function. It's working, if I define an object {ageTotal: 0} as the second argument. How can I implement this sum of age without defining a second argument property only using an empty object {}.

const users = [
  { name: 'Tyler', age: 28},
  { name: 'Mikenzi', age: 26},
  { name: 'Blaine', age: 30 }
];

// output as a *int*
const sumAge = users.reduce((totals, current) => {
  return totals + current.age;
}, 0);
console.log(sumAge);

// output as *object*
function getUserData (users) {
  return users.reduce((data, user) => {
    data.ageTotal += user.age
    return data;
  }, { ageTotal: 0 });
}
console.log(getUserData(users));

I'm afraid I'm having trouble understanding the question. What result do you want? What's the problem you're having getting that result? Or what do you want to change about the code? — T.J. Crowder
– T.J. Crowder, Commented Jun 10, 2020 at 14:44
If you read my post, I hope you will get it. The title is a bit confusing. — Mamunur Rashid
– Mamunur Rashid, Commented Jun 10, 2020 at 14:58
You can use the same code as sumAge. Instead of returning the int, return an object with that as a property: const getUserData = users => ({ ageTotal: users.reduce((totals, current) => totals + current.age, 0) }) — adiga
– adiga, Commented Jun 10, 2020 at 15:08
@MamunurRashid - I read your post before posting the comment. Twice, in fact. You really shouldn't assume people haven't read your post. — T.J. Crowder
– T.J. Crowder, Commented Jun 10, 2020 at 16:54

Yevhen Horbunkov · Accepted Answer · 2020-06-10 14:51:01Z

1

You may use short-circuit evaluation while incrementing to add current age value to accumulator property ageTotal (if it exists, or set it to 0, otherwise):

data.ageTotal = (data.ageTotal || 0) + user.age

Following is a quick demo:

const users = [
  { name: 'Tyler', age: 28},
  { name: 'Mikenzi', age: 26},
  { name: 'Blaine', age: 30 }
];

// output as *object*
function getUserData (users) {
  return users.reduce((data, user) => {
    data.ageTotal = (data.ageTotal || 0) + user.age
    return data;
  }, {});
}
console.log(getUserData(users));

Or, if you seek to make your syntax more concise:

const users = [
  { name: 'Tyler', age: 28},
  { name: 'Mikenzi', age: 26},
  { name: 'Blaine', age: 30 }
];

// output as *object*
const getUserData = users =>
  users.reduce((data, {age}) => 
    (data.ageTotal = (data.ageTotal || 0) + age, data), {});

console.log(getUserData(users));

edited Jun 10, 2020 at 14:51

answered Jun 10, 2020 at 14:45

Yevhen Horbunkov

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1 Comment

Mamunur Rashid Over a year ago

Thanks @Yevgen Gorbunkov

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