How to find the sum of the array properties' values of objects from the array?

Question

I have an array of countries and populations. How can I withdraw the amount of population in all countries?

[
  { name: 'Poland', population: 42 000 000},
  { name: 'Belarus', population: 9 500 000},
  { name: 'Moldova', population: 3 500 000},
  { name: 'Switzerland', population: 8 400 000}
]

function calculateAverageCountryPopulation(countries) {

}

The sum of the array elements is not difficult. But I don't know how to do this task.

var arr = [3, 2, 5, 6];

function arraySum(array) {
  var sum = 0;
  for (var i = 0; i < array.length; i++) {
    sum += array[i];
  }
  console.log(sum);
}
arraySum(arr);

score 0 · Answer 1 · answered Dec 16 '19 at 17:25

0

function calculateAverageCountryPopulation(countries) {
  return countries.map(x => x.population).reduce((acc, y) => acc + y)
}

answered Dec 16 '19 at 17:25

Michael Ossig

205
2
9

Thanks its working - can you give me a link to read more about this solution? Thank you! – Viktor Nomad Dec 16 '19 at 17:28
This is not the average. – Bibberty Dec 16 '19 at 17:30
@Bibberty correct, the question asked for the sum – Michael Ossig Dec 16 '19 at 17:31
@PerryNomad https://stackoverflow.com/questions/4244896/dynamically-access-object-property-using-variable – Michael Ossig Dec 16 '19 at 17:31
1

Yes, but the the function name .... :) – Bibberty Dec 16 '19 at 17:32
@Bibberty lol, and here we also learn the importance of properly naming your functions! – Michael Ossig Dec 16 '19 at 17:32
Yea you both are right! the sum is - understand for me - and how to calculate average population of the countries? – Viktor Nomad Dec 16 '19 at 17:44
@PerryNomad take the sum and divide it by the length of the array – Michael Ossig Dec 16 '19 at 17:52

score 0 · Answer 2 · answered Dec 16 '19 at 17:25

Use a reduce and divide.

const data = [
  { name: 'Poland', population: 42000000},
  { name: 'Belarus', population: 9500000},
  { name: 'Moldova', population: 3500000},
  { name: 'Switzerland', population: 8400000}
]
const calculateAverageCountryPopulation = (countries) => countries.reduce((a,{ population: p}) => a+=p,0)/countries.length;

console.log(calculateAverageCountryPopulation(data));

How to find the sum of the array properties' values of objects from the array?

2 Answers2