Create aggregation function to report most popular in Google DataTable - google-visualization

Question

I have a Google DataTable which looks like this:
var data = new google.visualization.DataTable();
data.addColumn('string', 'City');
data.addColumn('string', 'Model');
data.addColumn('number', 'Sold');
data.addRows([
["Melbourne","Ford",10],
["Perth","Ford",2],
["Melbourne","Ford",7],
["Melbourne","Holden",25],
["Perth","Holden",25],
["Melbourne","Holden",12],
["Melbourne","Ford",11]
]);
What I would like to do is group by City and report the Model with the highest cumulative Sold value for that City.
The result returned would be :
City Model
Melbourne Holden
Perth Ford
From my reading of the Google Visualisation API it is possible to write a custom aggregation function but that is beyond my limited experience.
Any assistance would be greatly appreciated.

Answer 1

This would require a double grouping: the first time to get total sold per model per city, and the second time to get the most popular model.
var g1 = google.visualization.data.group(data, [0, 1], [{
type: 'number',
label: 'Total Sold',
column: 2,
aggregation: google.visualization.data.sum
}]);
// create a view to merge columns 1 and 2 together for the grouping below
var view = new google.visualization.DataView(g1);
view.setColumns([0, {
type: 'string',
label: 'Model QTy Sold',
calc: function (dt, row) {
var o = {model: dt.getValue(row, 1), sold: dt.getValue(row, 2)};
return JSON.stringify(o);
}
}]);
var g2 = google.visualization.data.group(data, [0], [{
type: 'string'
label: 'Most Popular'
aggregation: function (values) {
var max = null, ret = null;
for (var i = 0; i < values; i++) {
var o = JSON.parse(values[i]);
if (max == null || o.sold > max) {
max = o.sold;
ret = o.model;
}
}
return ret;
}
}]);
g2 should contain model with highest sales grouped by city. If there is a tie between two models, this will return the first model in the values array (likely values will be ordered by model name, but this is not guaranteed).

Answer 2

The edits I made to asgallant's second grouping were:
var g2 = google.visualization.data.group(view, [0], [{
type: 'string',
label: 'Most Popular',
column: 1,
aggregation: function (values) {
var max = null, ret = null;
for (var i = 0; i < values.length; i++) {
var o = JSON.parse(values[i]);
if (max == null || o.sold > max) {
max = o.sold;
ret = o.model;
}
}
return ret;
}
}]);