Purchase items regrouping

gistfile1.js

var purchaseItems = [
  {
    "id":128449,
    "name":"Yellow Banana",
    "product_id":103672,
    "product_name":"Bananas",
    "purchase_date":"2014-02-09 00:00:00",
    "dvp_value":5.6,
    "nutrient_rate":124.0
    
  },
  {
    "id":128827,
    "name":"Bananas",
    "product_id":103672,
    "product_name":"Bananas",
    "purchase_date":"2014-02-13 00:00:00",
    "dvp_value":5.6,
    "nutrient_rate":124.0
  },
  {
    "id":140322,
    "name":"Bananas",
    "product_id":103672,
    "product_name":"Bananas",
    "purchase_date":"2014-03-03 00:00:00",
    "dvp_value":5.6,
    "nutrient_rate":124.0
  }
];

var groupedByProduct = [
  {
    product_id: 103672,
    product_name: "Bananas",
    dvp_value: 5.6,
    nutrient_rate: 124,
    purchase_items: [
      { id: 128449, name: "Yellow Banana", purchase_date: "2014-02-09 00:00:00" },
      { id: 128827, name: "Bananas", purchase_date: "2014-02-13 00:00:00" },
      { id: 140322, name: "Bananas", purchase_date: "2014-03-03 00:00:00" }
    ]
  }
];