Sum values of objects in array

Question

I would like to create a sum of an array with multiple objects.

Here is an example: var array = [{"adults":2,"children":3},{"adults":2,"children":1}];

How do I return the sum of adults and the sum of children into a new variable for each?

Thanks, c.

Answer 1

Use Array.prototype.reduce(), the reduce() method applies a function against an accumulator and each value of the array (from left-to-right) to reduce it to a single value.

var array = [{
  "adults": 2,
  "children": 3
}, {
  "adults": 2,
  "children": 1
}];

var val = array.reduce(function(previousValue, currentValue) {
  return {
    adults: previousValue.adults + currentValue.adults,
    children: previousValue.children + currentValue.children
  }
});
console.log(val);

Answer 2

 

var array = [{"adults":2,"children":3},{"adults":2,"children":1}];

var totalChild = array.reduce((accum,item) => accum + item.children, 0)

console.log(totalChild) //output 4

Answer 3

Seeing nobody posted this yet... here is a nice shorthand method:

.reduce((acc, curr) => acc + curr.property, 0)

Example:

arr = [{x:1, y:-1}, {x:2, y:-2}, {x:3, y:-3}];

x_sum = arr.reduce((acc, curr) => acc + curr.x, 0); // 6
y_sum = arr.reduce((acc, curr) => acc + curr.y, 0); // -6

Answer 4

You can write a function for this task, which gets the array to iterate over an the property, which value should be added.

The key feature of the function is the Array#reduce methode and a property which returns the actual count calue and the actual property value.

function count(array, key) {
    return array.reduce(function (r, a) {
        return r + a[key];
    }, 0);
}

var array = [{ "adults": 2, "children": 3 }, { "adults": 2, "children": 2 }],
    adults = count(array, 'adults'),
    children = count(array, 'children');

document.write('Adults: ' + adults + '<br>');
document.write('Children: ' + children + '<br>');