How to count json items for each param ?

[skylinezpromise]

I have a JSON store :

 {
        "Week": 1145,
        "Sev_Logged": 22,
        "From": "IN1"
    },
    {
        "Week": 1145,
        "Sev_Logged": "44",
        "From": "IN1"
    },
    {
        "Week": 1145,
        "Sev_Logged": 54,
        "From": "IN2"
    },
    {
        "Week": 1146,
        "Sev_Logged": "66",
        "From": "IN1"
    },
    {
        "Week": 1146,
        "Sev_Logged": "66",
        "From": "IN2"
    }

I want to count for each "Week", the number of "From", for example for Week 1146, i'd get IN1 = 1 and IN2 = 1 and for week 1145 i'd get IN1 = 2 and IN2 = 1.

I've written a function that loops through my data store to count IN1 and IN2 for each param:

countBy: function(param){
        var count = {};
        this.each(function(item){
            var type = item.get(param);
            if (Ext.isDefined(count[type])){
                count[type]++;
            } else {
                count[type] = 1;
            }                               
        });
        return count;
    }

But the problem is that when I give it "Week" in param, it doesn't count IN1 and IN2 for each WEEK, it returns "1145" : 3 and 1146 : 2, but what i want is : "1145" : {IN1 : 2} and "1146" : {IN1 : 1}.

Thank you for your help!

[vietits]

countBy: function(param){
    var count = {};
    this.each(function(item){
        var type = item.get(param);
        var from = item.get('from');
        count[type] = count[type] || {};
        if (Ext.isDefined(count[type][from])){
            count[type][from]++;
        } else {
            count[type][from] = 1;
        }                               
    });
    return count;
}