Question

I am currently putting together a simple application for inventory management using backbone. I have a table in my database that contains model and quantity; this is the strigify version of the object:

var invt =

[
{
“id”:1,
“model”:”Canon SX230″,
“qty”:10,
“price”:”150.50″
},
{
“id”:2,
“model”:”Canon Rebel T3i”,
“qty”:25,
“price”:”450.50″,
},
{
“id”:3,
“model”:”Canon Rebel T2″,
“qty”:10,
“price”:”250.00″
},
{
“id”:4,
“model”:”Canon Rebel T2i”,
“qty”:15,
“price”:”275.00″
},
{
“id”:5,
“model”:”Canon SX230″,
“qty”:5,
“price”:”125.00″
}]

How can I filter through to sum the quantities based on the model. Creating a new object with the similar models totaled quantity.

Essentially the result would be:
[{
“id”:1,
“model”:”Canon SX230″,
“qty”:15,
“price”:”275.00″
},
{
“id”:2,
“model”:”Canon Rebel T3i”,
“qty”:25,
“price”:”450.50″
}]
etc…

I’ve been trying to use the following loop:

var sum = {};

    for (var i = 0; i < invt.length; i++) { 
        var record = invt[i];

        sum.model = record.model + (sum.model);
    };

Answer 1

As you’ve used only JS related tags, I guess you want to do this client-side.

You can do it like this:

var records = [
    {
        id: 1,
        model: "A",
        quantity: 6
    }, {
        id: 1,
        model: "A",
        quantity: 4
    }, {
        id: 1,
        model: "B",
        quantity: 3
    }, {
        id: 1,
        model: "B",
        quantity: 2
    }
];

var sum = {};
for(var i = 0; i < records.length; i++) {
    var record = records[i];
    sum[record.model] = record.quantity + (sum[record.model] || 0);
}
document.body.innerHTML = JSON.stringify(sum);​

Demo: http://jsfiddle.net/Dhsm5/

It would be trivial to convert this object into the format you want.