Filter array of objects and sum their properties in Swift

Question

I would like to generate a shopping list from an array of products. I have an entity "Product" in Core Data that has name (String) and amount (Int) as its properties. I am in the moment where I have an array of products with some duplicates, something like that:

var products : [Product] = [Apple, Egg, Orange, Apple, Orange, Banana, Egg, Egg]

How can I filter such array to get sums of amount of specific products? I would like to get as a result the list of products with their amounts like: Apple: 4, Banana: 3, Egg: 7, Orange 2. I know that I can make a Set from that Array to avoid duplicates, but I don't know how to sum products' amount before that.

why do you have an array with dupes? why don't you merge when you add to the array ? — Wain
– Wain, Commented Jul 15, 2016 at 8:58

JMI · Accepted Answer · 2016-07-15 09:16:22Z

enum Product {
    case Apple
    case Egg
    case Orange
    case Banana
}

let products: [Product] = [.Apple, .Egg, .Orange, .Apple, .Orange, .Banana, .Egg, .Egg]

products.reduce([:]) { (map, product) -> [Product: Int] in
    var updatedMap = map
    if let value = map[product] {
        updatedMap[product] = value + 1
    }
    else {
        updatedMap[product] = 1
    }
    return updatedMap
} //[Orange: 2, Apple: 2, Egg: 3, Banana: 1]

same with strings:

let products: [String] = ["Apple", "Egg", "Orange", "Apple", "Orange", "Banana", "Egg", "Egg"]

products.reduce([:]) { (map, product) -> [String: Int] in
    var updatedMap = map
    if let value = map[product] {
        updatedMap[product] = value + 1
    }
    else {
        updatedMap[product] = 1
    }
    return updatedMap
} // ["Apple": 2, "Egg": 3, "Orange": 2, "Banana": 1]

Or by extension for all hashable sequence types:

extension SequenceType where Generator.Element: Hashable {
    func countElements() -> [Generator.Element : Int] {
        return reduce([:]) { (map, element) -> [Generator.Element : Int] in
            var updatedMap = map
            if let value = map[element] {
                updatedMap[element] = value + 1
            }
            else {
                updatedMap[element] = 1
            }
            return updatedMap
        }
    }
}

products.countElements() //["Apple": 2, "Egg": 3, "Orange": 2, "Banana": 1]

7stud · Accepted Answer · 2016-07-15 10:47:06Z

enum Fruit {
    case Orange
    case Lemon
    case Potato
}

let fruits = [Fruit.Orange, .Lemon, .Potato, .Orange, .Lemon, .Orange]

var result: [Fruit: Int] = [:]

for fruit in fruits {
    if let count = result[fruit] {
        result[fruit] = count + 1
    }
    else {
        result[fruit] = 1
    }
}

print(result)

--output:--
[Fruit.Potato: 1, Fruit.Orange: 3, Fruit.Lemon: 2]

Or, even:

num Product {
    case Apple
    case Egg
    case Orange
    case Banana
}

let products: [Product] = [.Apple, .Egg, .Orange, .Apple, .Orange, .Banana, .Egg, .Egg]

let result = products.reduce([:]) { (var map, product) -> [Product: Int] in
    if let count = map[product] {
        map[product] = count + 1
    }
    else {
        map[product] = 1
    }

    return map
}

print(result)

--output:--
[Product.Orange: 2, Product.Apple: 2, Product.Egg: 3, Product.Banana: 1]

Khiem Tran · Accepted Answer · 2016-07-15 10:48:30Z

-1

You can do like this:

enum Fruit {
  case Orange
  case Lemon
  case Potato
}

let fruits = [Fruit.Orange, .Lemon, .Potato, .Orange, .Lemon, .Orange]
let fruitSet = Set(fruits)
var result = [Fruit: Int]()

for fruit in fruitSet {
  result[fruit] = fruits.filter { $0 == fruit }.count
}

someone please explain why my answer is not useful? The output will be [Fruit.Orange: 3, Fruit.Lemon: 2, Fruit.Potato: 1]

edited Jul 15, 2016 at 10:48

answered Jul 15, 2016 at 9:06

Khiem Tran

6,16916 silver badges25 bronze badges

2 Comments

7stud Over a year ago

Let's say you have an array that has 1 million elements containing 20,000 different fruits. How many times would your algorithm have to traverse the 1 million element array?

OldManMcDonalds Over a year ago

You must have a big household 7stud.... The question was about a shopping list. :)

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