像购物清单一样格式化数组

Question

我有一个格式如下的数组：

["Trousers : 15.50", "Trousers : 15.50", "Jumper : 12.99", "Shoes: 50.00"]

我想这样格式化：

["2x Trousers : 31.00", "1x Jumper : 12.99", "1x Shoes: 50.00"]

我尝试使用以下格式进行格式化：

 var counts: [String:Int] = [:]
 var shoppingList = ["Trousers : 15.50", "Trousers : 15.50", "Jumper : 12.99", "Shoes: 50.00"]
 var formattedShoppingList = [String]()

     for item in shoppingList {
         counts[item] = (counts[item] ?? 0) + 1
     }


     for (key, value) in counts {

         let display:String = String(value) + "x " + key
         formattedShoppingList.append(display)

     }

但我明白了

["2x Trousers : 15.50", "1x Jumper : 12.99", "1x Shoes: 50.00"]

如果我使用字典，我不能有重复。我该如何处理？

Answer 1

我会创建一个结构来表示商品名称/价格对（可能还有未来的其他数据，例如库存数量）。

struct Item: Hashable {
    let name: String
    let price: Double

    public var hashValue: Int { return name.hashValue ^ price.hashValue }

    public static func ==(lhs: Item, rhs: Item) -> Bool {
        return lhs.name == rhs.name && rhs.price == rhs.price
    }
}

let shoppingList = [
    Item(name: "Trousers", price: 15.50),
    Item(name: "Trousers", price: 15.50),
    Item(name: "Jumper", price: 12.99),
    Item(name: "Shoes", price: 50),
]

let counts = shoppingList.reduce([Item: Int]()){counts, item in
    var counts = counts
    counts[item] = (counts[item] ?? 0) + 1
    return counts
}

let formattedShoppingList = counts.map{ item, count in "\(count)x \(item.name): £\(item.price)" }

print(formattedShoppingList)

[“2x 裤子：15.5 英镑”，“1x 鞋子：50.0 英镑”，“1x 套头衫：12.99 英镑”]

Answer 2

你可以使用这个结构，它接受你的字符串作为构造函数的参数：

struct ShoppingItem: Hashable {
    let name: String
    let price: NSDecimalNumber

    //Expects a String in the form "ElementName : Price"
    init?(description: String) {
        let splitDescription = description.components(separatedBy: ":")

        guard splitDescription.count == 2 else { return nil }

        name = splitDescription[0].trimmingCharacters(in: CharacterSet.whitespacesAndNewlines)
        price = NSDecimalNumber(string: splitDescription[1])
    }

    public var hashValue: Int {
        return "\(name)\(price)".hashValue
    }
}
func ==(lhs: ShoppingItem, rhs: ShoppingItem) -> Bool {
    return lhs.hashValue == rhs.hashValue
}

有了它，你可以将你的购物清单转换成这样的购物清单（考虑到，这会丢弃它无法转换的项目，你可以检查 nil 项目以确保所有项目都可以转换） ：

var shoppingItems = shoppingList.flatMap(ShoppingItem.init(description:))

然后，你只是做你之前所做的，只是在最后乘以价格：

var counts = [ShoppingItem: Int]()
for item in shoppingItems {
    counts[item] = (counts[item] ?? 0) + 1
}

for (key, value) in counts {
    let multipliedPrice = key.price.multiplying(by: NSDecimalNumber(value: value))
    let display = "\(value)x \(key.name) : \(multipliedPrice)"
    formattedShoppingList.append(display)
}

Answer 3

对于简单的对，您不需要结构或类；使用元组数组：

    var shoppingList = [("Trousers", 15.50), ("Trousers", 15.50), ("Jumper", 12.99), ("Shoes", 50.00)]

    for (name, price) in shoppingList {
        print(name, price)
    }