Try this http://jsbin.com/sahasira/1/edit
total_value_year = [
['2014', 1500],
['2015', 1000],
['2014', 150],
['2015', 200],
['2015', 50]
];
var arr = {};
total_value_year.forEach(
function (item, index) {
arr[item[0]] = (arr[item[0]] || 0) + item[1];
}
);
console.log(arr["2014"]);
console.log(arr["2015"]);