var data = [{'id': 1, 'amount': 123, 'currency': 'CHF'}, {'id': 2, 'amount': 321, 'currency': 'USD'}, {
'id': 3,
'amount': 4324,
'currency': 'UAH'
}, {'id': 4, 'amount': 45645, 'currency': 'USD'}, {'id': 5, 'amount': 8972, 'currency': 'CHF'}];
var newData = [];
for (i = 0; i < data.length; ++i) {
if (typeof newData[data[i]['currency']] == 'undefined')
newData[data[i]['currency']] = 0;
newData[data[i]['currency']] += data[i]['amount'];
}
for (var key in newData) {
console.log(key + ' ' + newData[key]);
}