Loop through array of objects and return sum of each total values by object element id

Question

I\'m calculating taxes for a very complicate invoicing approach. I can\'t explain the whole process but if you have questions I will answer as best as I can

Answer 1

I think Array.prototype.reduce will be your best bet for this:

var totals = data.reduce(function(c,x){
    if(!c[x.tax_id]) c[x.tax_id] = {
        tax_name: x.tax_name,
        tax_id: x.tax_id, 
        total_tax: 0
    };
    c[x.tax_id].total_tax += Number(x.tax_value);
    return c;
}, {});

This approach generates an object that has, as its properties, the tax ID numbers. If you really want a flat array from that, you can convert that into an array after the fact:

var totalsArray = [];
for(var taxId in totals){
    totalsArray.push(totals[taxId]):
}

Demonstration: http://jsfiddle.net/3jaJC/1/

Answer 2

Use the reduce method:

selected_taxes.reduce(function (p, c) {
    if (p[c["tax_id"]]) {
        p[c["tax_id"]]["total_tax"] += +c["tax_value"];
    } else {
        p[c["tax_id"]] = {
            "tax_name": c["tax_name"],
            "total_tax": +c["tax_value"]
        }
    }
    return p;
}, {});

This returns a new object containing the desired data:

{
    "1": {
        "tax_name": "GST 5%",
        "total_tax": 26.46
    },
    "2": {
        "tax_name": "HST 13%",
        "total_tax": 34.39
    },
    "3": {
        "tax_name": "QST 9.975%",
        "total_tax": 52.76
    }
}

DEMO

Answer 3

When you're looping over the objects, see what taxId it is and generate a sum for each different taxId.

var sums = {}, obj, i;
for (i = 0; i < selected_taxes.length; i++){
    obj = selected_taxes[i];
    if (!sums[obj.tax_id]) {
        sums[obj.tax_id] = 0;
    }
    sums[obj.tax_id] += +obj.tax_value;
}
console.log(sums); //{ 1:26.46, 2:34.39, 3: 52.76}

http://jsfiddle.net/4X6Wb/

Answer 4

My solution using typed arrays:

var sum_arr = new Float32Array(arr.length); for (var i = 0; i < arr.length; i++){ var tax_id = arr[i].tax_id; sum_arr[tax_id] += parseFloat(arr[i].tax_value); }

jsfidle: http://jsfiddle.net/LJ7Nd/

The idea: assume you have n tax_ids. Create an array of length n called sum_arr. Pull the tax_id at each iteration and increment that particular slot in the array by the corresponding tax_value. Then when you want the sum of all tax_values of tax_id = 1 you simply index sum_arr[1].