Sum values of objects in array [duplicate]

Question

This question already has answers here:

Better way to sum a property value in an array (20 answers)

Closed last month.

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.

• RomanPerekhrest: 'into a new variable for each' means a single variable or different variables for each of essences?
• Pat Myron: similar: Better way to sum a property value in an array

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);

• Rayon: Its just your assumption Buddy..I read your answer when I saw your comment.. If you go through the revisions of my answer, you will come to know..I commented object part in one of the version but later I thought it will make more sense to return it as object than array..I am ready to delete this answer if you want me to... How much difference it is going to make ?
• T J: Well maybe. This is a silly answer and there is no edit history so I'll just remove mine. But this won't be the case always, So when you're gonna modify an answer, keep an eye out to see whether someone's answer already covers what you're modification does. Because in that case it's just duplication and can also be considered plagiarism, both aren't encouraged in this site as far as I know.
• Rayon: Well, Shall I always keep on reading others answers before editing ? And What do I do If I find mine edited answer identical with others answer who answered later ? Any other recommendations sir ? _Can you PROVE _ that I have copied your answer. Can you ? I will suggest you to post an answer if it makes immense difference that the answer which is already posted.. You are free to post as many answers as you want but that will not gain any attention... Let other viewers decide how to treat copied answers..
• Rayon: @NickSteele - Your comment made me go through it all over again. Bad old days! :P
• Rayon: @NickSteele - Sorry to reply to you so late. jsfiddle.net/rayon_1990/63cmh0xt

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

• Sebastian Simon: "Seeing nobody posted this yet" — It’s the same as the answer by DINESH Adhikari.

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>');

Answer 5

var array = [{"adults":2,"children":3},{"adults":2,"children":1}];
var sumProps = prop => (sum, obj) => sum += obj[prop];
var adultsCount = array.reduce( sumProps('adults'));
var childrenCount = array.reduce( sumProps('children'));

Answer 6

To get a sum of each essence into separate variable:

var array = [{"adults":2,"children":3},{"adults":2,"children":1}];
var adults_sum = 0, children_sum = 0;
array.forEach(function(obj){
 adults_sum += obj["adults"];
 children_sum += obj["children"];
});
console.log(adults_sum, children_sum); // 4 4

Answer 7

We are not writing code for you, but I suppose you should try:

var val = array.reduce(function (sum, tuple) {
 return { adults: sum.adults + tuple.adults,
 children: sum.children + tuple.children };
});

Answer 8

Here is a fun exercise in functional programming. Assuming you already have a sum function for simple arrays of numbers, you can implement a function that will sum the totals of all keys over an array of objects in just two expressions. No loops, hardcoded property names, anonymous functions or if/else required. I adopted the following code from my answer to How to get an object containing the sum of all items in an arrays of objects? :

var add = (a, b) => a + b;
var sum = _.partial(_.reduce, _, add, 0);
function sumByProperties(data) {
 var keys = _.chain(data)
 .map(_.keys).flatten().uniq().value();
 return _.chain(keys).zip(keys).object()
 .mapObject(_.property)
 .mapObject(_.partial(_.map, data))
 .mapObject(_.compose(sum, _.compact))
 .value();
}
console.log(sumByProperties([{
 apple: 1,
 banana: 4,
 fish: 2,
 melon: 3,
}, {
 apple: 3,
 banana: 2,
 fish: 5,
 melon: 1,
}]));

<script src="https://cdn.jsdelivr.net/npm/[email protected]/underscore-umd-min.js"></script>

While the implementation of sumByProperties is not straightforward, figuring out how it works will deepen your understanding of functional programming. This will empower you to write some things very concisely, such as the definition of sum at the top.

For the convenience of the reader, here are links to the documentation of each Underscore function used in this snippet, by order of evaluation:

_.partial _.reduce _.chain _.map _.keys _.flatten _.uniq _.value _.zip _.object _.mapObject _.property _.partial _.compose _.compact

Answer 9

May be it can help you and this also without use reduce func.

var sumAdult=0;
var sumChildren=0;
var array = [{
 "adult": 2,
 "children": 3
}, {
 "adult": 2,
 "children": 1
}];
 function x(a,b){
 return a+b;
 }
for (y in array){ 
 sumAdult=x(0, array[y].adult);
 console.log( "adult :" + sumAdult);
 sumChildren=x(0, array[y].children);
 console.log( "children :" + sumChildren);
}