Formatting an array like a shopping list

Question

I have an array formatted like this:

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

I would like to format it like this:

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

I tried formatting using this:

 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)

     }

But I get this

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

If I use a dictionary I cannot have duplicates. How shall I proceed with this?

Answer 1

I would make a struct to represent Item name/price pairs (and perhaps other data in the future, like quantity in stock, for example).

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 Trousers: £15.5", "1x Shoes: £50.0", "1x Jumper: £12.99"]

Answer 2

You could use this struct, which accepts your strings as parameter for the constructor:

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
}

With it, you could convert your shopping list, to a list of shopping items like this (take into account, that this discards items it can't transform, you could check for nil items to make sure all could be converted):

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

and then, you just do what you did before, only multiplying the price at the end:

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

You don't need a struct or class for a simple pair; use an array of tuples:

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

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