Dart: How to sort a list of objects by values in their nested map

Question

I'm having trouble sorting a list of objects by the highest value in a nested map in each. I've looked through many similar questions here on SO but am none the wiser. Any help would be greatly appreciated.

My list looks like this:

{
  "stores": [
    {
      "id": 305,
      "title": "Store 1",
      "discounts": [
        {
          "id": 335,
          "category": "Books",
          "type": "percentage",
          "minDiscount": 0,
          "maxDiscount": 1.25
        },
        {
          "id": 337,
          "category": "Gift cards",
          "type": "percentage",
          "minDiscount": 0,
          "maxDiscount": 8.5
        },
        {
          "id": 338,
          "category": "Merchandise",
          "type": "percentage",
          "minDiscount": 0,
          "maxDiscount": 2.5
        }
      ]
    },
    {
      "id": 304,
      "title": "Store 2",
      "discounts": [
        {
          "id": 340,
          "category": "New Customer",
          "type": "percentage",
          "minDiscount": 0,
          "maxDiscount": 5
        },
        {
          "id": 339,
          "category": "Existing Customer",
          "type": "percentage",
          "minDiscount": 0,
          "maxDiscount": 2.5
        }
      ]
    },
    {
      "id": 303,
      "title": "Store 3",
      "discounts": [
        {
          "id": 341,
          "category": "General",
          "type": "percentage",
          "minDiscount": 0,
          "maxDiscount": 7.3
        }
      ]
    },
    {
      "id": 302,
      "title": "Store 4",
      "discounts": [
        {
          "id": 333,
          "category": "New customers",
          "type": "percentage",
          "minDiscount": 0,
          "maxDiscount": 3
        }
      ]
    },
    {
      "id": 301,
      "title": "Store 5",
      "discounts": [
        {
          "id": 332,
          "category": "General",
          "type": "percentage",
          "minDiscount": 0,
          "maxDiscount": 9
        }
      ]
    }
  ]
}

My expected result is the stores listed based on highest discount available in each of their 'discounts' Map property. The output:

1. Store 5 (9 % highest)
2. Store 1 (8.5 % highest)
3. Store 3 (7.3 % highest)
4. Store 2 (5 % highest)
5. Store 4 (3 % highest)

Answer 1

You can try this approach, if your desired output is:

• Store 5
• Store 1
• Store 3
• Store 2
• Store 4

stores.sort((a, b) {
    List discountsInA = a["discounts"];
    List discountsInB = b["discounts"];
    dynamic maxDiscountInA = discountsInA.fold<dynamic>(
        0, (max, e) => e['maxDiscount'] > max ? e['maxDiscount'] : max);
    dynamic maxDiscountInB = discountsInB.fold<dynamic>(
        0, (max, e) => e['maxDiscount'] > max ? e['maxDiscount'] : max);
    return maxDiscountInA > maxDiscountInB
        ? -1
        : maxDiscountInA < maxDiscountInB
            ? 1
            : 0;
  });