Adding numbers in a object array

Question

var numbers = [{grades:[100,100,100]}];
var result = 0;

for (var i=0;i<numbers.length;i++){
    for (var p in numbers.grades[i]);

    result+=p+":"+numbers[i][p];
    //console.log(p+":"+numbers[i][p])
    console.log(result);
}

this is what i have so far. I know how to get all the numbers in the .grades but i want them all added up in a very simple way.

Answer 1

The problem you have is numbers.length is only 1 . You want

numbers[0].grades.length; // 3

This should sum the grades for you

for (var i=0, sum=0; i<numbers[0].grades.length; i++) {
  sum += numbers[0].grades[i];
}

sum; // 300

---

If you have access to Array.prototype.reduce , you could use this

var sum = numbers[0].grades.reduce(function(a, b) { return a +  b; }, 0);

sum; // 300

Note .reduce requires ECMAScript >= 5 and will not work in IE <= 8

Answer 2

You almost had it

var numbers = [{grades:[100,100,100]}];
var result = 0;

for (var i=0;i<numbers.length;i++){
    for (var g=0; g<numbers[i].grades.length; g++) {

    result = result+numbers[i].grades[g];
    console.log(result);
    }
}

As discussed, if it does support ES5, you can write it like this:

var numbers = [{grades:[100,100,100]}];
var result = 0;

numbers.forEach( function(val) {
    result = result + val.grades.reduce( function (previousValue, currentValue, index, array) {
        return previousValue + currentValue;
    })
});

just remember that you need to loop through the numbers array, instead of giving it a default value of '0' // numbers[0]grades etc

Answer 3

or you can try:

for(var j=0; j<numbers.length;j++)
{
  for (var i=0, sum=0; i<numbers[j].grades.length; i++) {
    sum += numbers[j].grades[i];
  }
}
console.log(sum);

Answer 4

The list you want to loop through is :

var list = numbers[0].grades;

Then, inside the loop :

result += list[i];

That's it :)

---

How to browse a javascript array :

var a = ['I', 'need', 'the', 'basics'];
console.log(a[0]); // "I"
console.log(a[3]); // "basics"
console.log(a[a.length - 1]); // "basics"

How to browse a javascript object :

var o = { a: 'I', b: 'need', c: 'the', d: 'basics' };
console.log(o.a); // "I"
console.log(o.d); // "basics"
console.log(o['d']); // "basics"

All together :

var mixed = [{ a: 'foo' }, { b: 'bar' }, { c: ['baz'] }];
console.log(mixed[0].a); // "foo"
console.log(mixed[1].b); // "bar"
console.log(mixed[2].c[0]); // "baz"

---

To add up all grades :

var grades, i, j;
var sum = 0;
var list = [
    { grades: [1, 2, 3] },
    { grades: [4, 5, 6] }
];

for (i = 0; i < list.length; i++) {
    grades = list[i].grades;
    for (j = 0; j < grades.length; j++) {
        sum += grades[j];
    }
}

console.log(sum); // 21

Answer 5

A more functional/javascript approach would be to use array.reduce() :

var sum = numbers[0].grades.reduce(function(previousValue, currentValue, index, array){
    return previousValue + currentValue;
});

console.log(sum);