Sum of object properties within an array

Question

I have an array with properties, take the following for example:

var arrayPeople = [
    {
        name: 'joe',
        job: 'programmer',
        age: 25,
    },
    {
        name: 'bob',
        job: 'plumber',
        age: 30,
    };
];

I want to create a function that will return their average ages, here is what i have that is currently not working

var ageAverage = function(array) {
    var age = 0, average;
    for (var i = 0; i < array.length; i++) {
        age += array[i].age;
    }
    average = age / array.length;
    return average;
};

What I am getting when running this function is Not A Number

But what I can get to work is:

var ageAverage = function(array) {
    var age = 0, average;
    for (var i = 0; i < array.length; i++) {
        age = array[0].age;
    }
    average = age / array.length;
    return average;
};

The subtle difference here is that I took away the += and just made it =, and i took away the use of our variable i and just gave it the first index of the array. So in doing this, I know that the function is correctly substituting the parameter array with arrayPeople, but there is something going wrong in my for loop that is stopping i from becoming 0 and 1 (the indexes of arrayPeople).

P.S. I am trying to do this on my own, and I am not looking for someone to just do the problem for me, I would really appreciate just some hints on what to fix or maybe a concept I need to research the understand how to fix this problem.

Thanks!!

Answer 1

Consider using map and reduce:

arrayPeople.
  map(function(item){ return item.age; }).
  reduce(function(a, b){ return a + b; }, 0) / arrayPeople.length;

Or just the reduce as @KooiInc pointed out:

arrayPeople.reduce(function (a,b) { return a + b.age; }, 0) / arrayPeople.length;

---

A working Example:

var arrayPeople = [{
    name: 'joe',
    job: 'programmer',
    age: 25,
  }, {
    name: 'bob',
    job: 'plumber',
    age: 30,
  }],
  average = arrayPeople.reduce(function(a, b) {
    return a + b.age;
  }, 0) / arrayPeople.length;

document.write(average);

Answer 2

You need initialize age variable (var age = 0)

var arrayPeople = [{
  name: 'joe',
  job: 'programmer',
  age: 25,
}, {
    name: 'bob',
    job: 'plumber',
    age: 30,
}];

var ageAverage = function(array) {
  var age = 0,
      average;

  for (var i = 0; i < array.length; i++) {
    age += array[i].age;
  }

  average = age / array.length;
  return average;
};

console.log(
  ageAverage(arrayPeople)
);

in your variant, age variable equals undefined, and undefined += number (for example 25) returns NaN;

also change , to ; in this line

from

for (var i = 0, i < array.length; i++) {

to

for (var i = 0; i < array.length; i++) {