jquery array group by

Here's a plain javascript way to do it that collects the unique indexes in a map and totals them as it does, then regenerates the array with the totals:

abcArr = [["A", 10], ["B", 20], ["A",30],["C",40]];

var items = {}, base, key;
for (var i = 0; i < abcArr.length; i++) {
    base = abcArr[i];
    key = base[0];
    // if not already present in the map, add a zeroed item in the map
    if (!items[key]) {
        items[key] = 0;
    }
    // add new item to the map entry
    items[key] += base[1];
}

// Now, generate new array
var outputArr = [], temp;
for (key in items) {
    // create array entry for the map value
    temp = [key, items[key]]
    // put array entry into the output array
    outputArr.push(temp);
}

// outputArr contains the result

Working demo: http://jsfiddle.net/jfriend00/vPMwu/

---

Here's a way using jQuery's .each:

abcArr = [["A", 10], ["B", 20], ["A",30],["C",40]];

var items = {}, base, key;
$.each(abcArr, function(index, val) {
    key = val[0];
    if (!items[key]) {
        items[key] = 0;
    }
    items[key] += val[1];
});

var outputArr = [];
$.each(items, function(key, val) {
    outputArr.push([key, val]);
});

// outputArr contains the result
document.body.innerHTML = JSON.stringify(outputArr);

Working demo: http://jsfiddle.net/jfriend00/Q8LLT/

Underscore.js has groupBy, and the rest can be done by mapping over reduce (that is, reducing each group to one element

abcArr = [["A", 10], ["B", 20], ["A",30],["C",40]]

var grouped = _.groupBy(abcArr, function(x){return x[0]})
var result  = _.map(grouped, function(x){
    return _.reduce(x, function(x,y){
        return [y[0], x[1]+y[1]];
    }, [,0])
})

http://jsfiddle.net/srvKQ/

Or (minified)

abcArr = [["A", 10], ["B", 20], ["A",30],["C",40]]

var result = _.map(
    _.groupBy(abcArr, function(x){return x[0]}),
    function(x){return _.reduce(
        x, function(x,y){return [y[0], x[1]+y[1]]}, [,0]
)});

http://jsfiddle.net/srvKQ/1/