Is it possible to calculate observables with parameters in Knockout

Possible duplicate:
knockoutjs: can we create a dependObservable function with a parameter?

In my view model, I have a function that returns the sum of elements depending on the type of element:

var ViewModel = function(data) {
    var self = this;

    this.Results = ko.observableArray(data);

    this.totalPerType = function(type) {
        var total = 0;
        for (var index in self.Results()) {
            if (self.Results()[index].Type == type)
                total += self.Results()[index].Quantity;
        }

        return total;
    };
};

When the user edits one of the elements, the total value is not updated automatically, since it is not calculated. Is it possible to change the totalPerType function to a computed observable without having to enter a type parameter in the view model (saving it as a parameter)?

I created a script to make it easier to try something: http://jsfiddle.net/7PK9r/