"use strict";

var myArray = [{ "shop": "shop1", "item1": "my apple 1", "item2": "my carrot 1" }, { "shop": "shop1", "item1": "my apple 1", "item2": "my carrot 1" }, { "shop": "shop2", "item1": "my apple 0", "item2": "my carrot 0" }, { "shop": "shop2", "item1": "my apple 0", "item2": "my carrot 1" }];
var MyArrayDefinition = [{ "item": "my apple 0", "color": "red", "group": "fruit", "score": 0 }, { "item": "my carrot 1", "color": "orange", "group": "vegetable", "score": null }, { "item": "my apple 1", "color": "red", "group": "fruit", "score": 1 }, { "item": "my carrot 0", "color": "orange", "group": "vegetable", "score": 0 }];

var k = Object.keys;
var items = MyArrayDefinition.reduce(function (o, v) {
  return o[v.item] = v, o;
}, {});

var shops = myArray.reduce(function (o, v, i, s) {
  return s = v[k(v).find(function (k) {
    return k;
  })], s = o[s] || (o[s] = {
    fruit: 0,
    vegetable: 0
  }), k(v).forEach(function (k) {
    return k.includes('item') && (s[(i = items[v[k]]).group] += i.score);
  }), o;
}, {});

// Helper function that calculates percentage
function percentage(amount, total) {
  if (total === 0) {
    // added check for 0 divisor
    return "0%";
  }
  return amount / total * 100 + "%";
}

var result = k(shops).map(function (k, i) {
  var total = Object.values(shops[k]).reduce(function (a, b) {
    return a + b;
  }) | 0; // added check if number else 0
  var fruit = shops[k].fruit | 0; // added check if number else 0
  var veg = shops[k].vegetable | 0; // added check if number else 0
  return {
    id: i + 1,
    shop: k,
    fruit: fruit,
    vegetable: veg,
    total: total,
    fruitPercentage: percentage(fruit, total),
    vegetablePercentage: percentage(veg, total)
  };
});

console.log(JSON.stringify(result, null, 2));

/** result from console.log()
 *
   [
     {
       "id": 1,
       "shop": "shop1",
       "fruit": 2,
       "vegetable": 2,
       "total": 4,
       "fruitPercentage": "50%",
       "vegetablePercentage": "50%"
     },
     {
       "id": 2,
       "shop": "shop2",
       "fruit": 2,
       "vegetable": 0,
       "total": 2,
       "fruitPercentage": "100%",
       "vegetablePercentage": "0%"
     }
   ]
 * */