Group object properties by common values with javascript

Question

I have the below js see this fiddle.

    var name = ["Ted", "Sarah", "Nancy", "Ted", "Sarah", "Nancy"];
    var prodID = [111, 222, 222, 222, 222, 222];
    var prodName = ["milk", "juice", "juice", "juice", "juice", "juice"];
    var qty = [1, 2, 3, 3, 3, 1];
    var data = {};
    for (i = 0; i < name.length; i++) {
        if (!data[name[i]]) {
            purchased = {
                "name": name[i],
                "prodID": prodID[i],
                "prodName": prodName[i],
                "qty": qty[i]
            };
            data[name[i]] = purchased;
        } else {
            purchased = data[name[i]];
            purchased.qty += +qty[i];
        }
        data[name[i]] = purchased;
    }
    data = $.map(data, function (val, key) {
        return val;
    });
    data.sort();
    $.each(data, function (i, val) {
        var plural = "";
        if (val.qty > 1) {
            plural = "'s";
        }
    $('body').append(val.name + ' has purchased ' + val.qty + ' bottle' + plural + ' of ' + val.prodName + '<br>');
    });

Which outputs

Ted has purchased 4 bottle's of milk
Sarah has purchased 5 bottle's of juice
Nancy has purchased 4 bottle's of juice

What I want to do is show each of the products they have purchased and how many of each.

eg looking at the above Ted has purchased 1 milk and 3 bottle's of juice, but I am currently outputing Ted has purchased 4 bottle's of milk as 4 is the total qty of his purchases.
How can I group it by each prodID/ProdName so that I get the below.

Ted has purchased 1 bottle of milk and 3 bottle's of juice
Sarah has purchased 5 bottle's of juice
Nancy has purchased 4 bottle's of juice

your data structure seems a little odd. Is there a reason you're using 4 arrays and linking the data by index? An object would be much better suited to this. — Rory McCrossan
– Rory McCrossan, Commented Jun 10, 2014 at 9:14
thanks for the feedback, I will look into this, if I console.log(purchased) in the for loop it tells me I am getting an object? am I misinterpreting what I am seeing in the console.log here? — ak85
– ak85, Commented Jun 10, 2014 at 9:31
@ak85: purchased is indeed an object. The remark was about the initial 4 arrays : you would be better off using one single array holding objects. — LeGEC
– LeGEC, Commented Jun 10, 2014 at 10:16

georg · Accepted Answer · 2014-06-10 10:27:35Z

The first step is to convert the data structure to something more appropriate, for example:

name.forEach(function(nam, i) {
    data[nam] = data[nam] || {};
    pid = prodID[i];
    data[nam][pid] = data[nam][pid] || {total:0, pname: prodName[i]};
    data[nam][pid].total += qty[i];
});

which gives you

 "Ted": {
  "111": {
   "total": 1,
   "pname": "milk"
  },
  "222": {
   "total": 3,
   "pname": "juice"
  }
 },
 "Sarah": {
  "222": {
   "total": 5,
   "pname": "juice"
  }
 },
 "Nancy": {
  "222": {
   "total": 4,
   "pname": "juice"
  }
 }

Given this, generating the output is pretty straightforward:

message = Object.keys(data).map(function(nam) {
    var purchases = data[nam];
    return nam + ' got ' + Object.keys(purchases).map(function(pid) {
        return purchases[pid].total + ' bottle(s) of ' + purchases[pid].pname
    }).join(' and ');
}).join(' <br> ');

http://jsfiddle.net/yP6X5/1/

(pluralization left as an exercise, do note however that the correct form is bottles, not bottle's).

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