CODEWITHSUNDEEP
javascriptarrays
bejewelled
bejewelled

Reputation: 305

How to sum up properties of an array of objects with reduce

Say I have the following array:

var BUILDINGS = [
    { production: {"numberProd": 6}},
    { production: {"numberProd": 11}},
    { production: {"numberProd": 14}},
];

I'm trying to use reduce() to add up the sum of these productions. I've tried to the following:

BUILDINGS.reduce(function(a,b) {return a.production.numberProd + b.production.numberProd});

But when I run the code I get the value NaN.

I was wondering how to properly set up the reduce() statement. Thank you!

Upvotes: 0

Views: 108

Answers (3)

Mamun
Mamun

Reputation: 68933

You have to pass initial value of 0 which will be assigned to the first parameter a in the initial iteration of reduce().

Try the following:

var BUILDINGS = [
    { production: {"numberProd": 6}},
    { production: {"numberProd": 11}},
    { production: {"numberProd": 14}},
];
var prod = BUILDINGS.reduce(function(a,b) {
  return a + b.production.numberProd;
}, 0);

console.log('Total:', prod);

Upvotes: 5

Isaac
Isaac

Reputation: 11805

You were very close:

BUILDINGS.reduce(function(a,b) {return a + b.production.numberProd}, 0);

BUILDINGS.reduce((currentValue, nextBuilding) => {
  return currentValue + nextBuilding.production.numberProd
}, 0) // 0 is the first value

Upvotes: 1

31piy
31piy

Reputation: 23859

You can do it like this:

var BUILDINGS = [
    { production: {"numberProd": 6}},
    { production: {"numberProd": 11}},
    { production: {"numberProd": 14}},
];

console.log(BUILDINGS.reduce((sum, item) => {
  sum += item.production.numberProd;
  return sum;
}, 0));

If you don't pass the initial value as 0, you will get a NaN as the result.

Upvotes: 0

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