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up vote 10 down vote favorite

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

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]);

I am wondering if it is possible to sum the number values found in the array (ex. 0+0+21+2+0 and so on) and have probably a variable with the result that I can use outside of the script tag because I have 7 of this kind of arrays corresponding for each of the day in the week. I want to make a comparison afterwards based on that. That is the most preferred method for this kind of actions if is possible?

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Iterate over the array and add the second elements of the inner arrays. –  Felix Kling Apr 17 '13 at 10:31
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6 Answers

up vote 1 down vote accepted

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
}

alert(myTotal); //22 in this instance
share|improve this answer
    
I think you meant myData[i][1]. And why use parseFloat if the value is already a number anyway? –  Felix Kling Apr 17 '13 at 10:35
    
it output 24156 instead of like it should 3. I've tested with an "empty value array" and I receive the same output... –  Daniela costina Vaduva Apr 17 '13 at 10:37
    
@FelixKling it works with myData[i][1] but how I make myTotal available in other script tag? –  Daniela costina Vaduva Apr 17 '13 at 10:39
    
Daniel, did you fix the typo that Felix Kling pointed out? Rember to write "myData[i][1]" instead of the wrong version: "myData[1]" in the example. –  Silas Hansen Apr 17 '13 at 10:39
    
@FelixKling Thanks have edited, and i guess i was being overprecautius by using parseFloat. Daniela i've tested and it works have a look here - jsbin.com/ibajas/1 –  Mark Walters Apr 17 '13 at 10:39
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up vote 24 down vote

You could use the Array.reduce method:

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

See MDN

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It should be prev[1] I guess. By all means the result won't give 23. –  VisioN Apr 17 '13 at 10:40
1  
@Kooilnc Please be aware that Array.reduce is an ECMAscript 5 addition so my not be supported by all browsers - see here developer.mozilla.org/en-US/docs/JavaScript/Reference/… which also includes some code which can be implemented to overcome this –  Mark Walters Apr 17 '13 at 10:41
    
@VisioN: forgot the initial value, added it. And no, it shouldn't be prev[1] @MarkWalters: yep, but one can use the shim from the MDN-link (see answer) –  KooiInc Apr 17 '13 at 10:47
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up vote 4 down vote

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

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up vote 0 down vote

The javascript built-in reduce for Arrays is not a standard, but you can use underscore.js:

var data = _.range(10);
var sum = _(data).reduce(function(memo, i) {return memo + i});

which becomes 

var sumMyData = _(myData).reduce(function(memo, i) {return memo + i[1]}, 0);

for your case. Have a look at this fiddle also.

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up vote 0 down vote

If you want to discard the array at the same time as summing, you could do (say, 'stack' is the array):

        var sum = 0;
        while(stack.lentgh > 0) sum += stack.pop();
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up vote 0 down vote

If you are looking for a nice modular clean way of doing it, I would say creating a sum method might 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 += 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
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