Sum values from an Array in JavaScript

Question

I have defined a JavaScript variables called myData which is a new Array like this:

var myData = new Array([\'2013-01-22\', 0], [\'         


        

Answer 1

I would use reduce

var myData = new Array(['2013-01-22', 0], ['2013-01-29', 0], ['2013-02-05', 0], ['2013-02-12', 0], ['2013-02-19', 0], ['2013-02-26', 0], ['2013-03-05', 0], ['2013-03-12', 0], ['2013-03-19', 0], ['2013-03-26', 0], ['2013-04-02', 21], ['2013-04-09', 2]);

var sum = myData.reduce(function(a, b) {
    return a + b[1];
}, 0);

$("#result").text(sum);

Available on jsfiddle

Answer 2

You can use the native map method for Arrays. map Method (Array) (JavaScript)

var myData = new Array(['2013-01-22', 0], ['2013-01-29', 0], ['2013-02-05', 0],
             ['2013-02-12', 0], ['2013-02-19', 0], ['2013-02-26', 0], 
             ['2013-03-05', 0], ['2013-03-12', 0], ['2013-03-19', 0], 
             ['2013-03-26', 0], ['2013-04-02', 21], ['2013-04-09', 2]);
var a = 0;
myData.map( function(aa){ a += aa[1];  return a; });

a is your result

Answer 3

Creating a sum method would work nicely, e.g. you could add the sum function to Array

Array.prototype.sum = function(selector) {
    if (typeof selector !== 'function') {
        selector = function(item) {
            return item;
        }
    }
    var sum = 0;
    for (var i = 0; i < this.length; i++) {
        sum += parseFloat(selector(this[i]));
    }
    return sum;
};

then you could do

> [1,2,3].sum()
6

and in your case

> myData.sum(function(item) { return item[1]; });
23

Edit: Extending the builtins can be frowned upon because if everyone did it we would get things unexpectedly overriding each other (namespace collisions). you could add the sum function to some module and accept an array as an argument if you like. that could mean changing the signature to myModule.sum = function(arr, selector) { then this would become arr

Answer 4

Try the following

var myData = [['2013-01-22', 0], ['2013-01-29', 1], ['2013-02-05', 21]];

var myTotal = 0;  // Variable to hold your total

for(var i = 0, len = myData.length; i < len; i++) {
    myTotal += myData[i][1];  // Iterate over your first array and then grab the second element add the values up
}

document.write(myTotal); // 22 in this instance