Finding sum of elements in Swift array

Question

What is the easiest (best) way to find the sum of an array of integers in swift? I have an array called multiples and I would like to know the sum of the multiples.

Answer 1

In Swift 4 You can also constrain the sequence elements to Numeric protocol to return the sum of all elements in the sequence as follow

extension Sequence where Element: Numeric {
    /// Returns the sum of all elements in the collection
    func sum() -> Element { return reduce(0, +) }
}

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edit/update:

Xcode 10.2 • Swift 5 or later

We can simply constrain the sequence elements to the new AdditiveArithmetic protocol to return the sum of all elements in the collection

extension Sequence where Element: AdditiveArithmetic {
    func sum() -> Element {
        return reduce(.zero, +)
    }
}

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Xcode 11 • Swift 5.1 or later

extension Sequence where Element: AdditiveArithmetic {
    func sum() -> Element { reduce(.zero, +) }
}

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let numbers = [1,2,3]
numbers.sum()    // 6

let doubles = [1.5, 2.7, 3.0]
doubles.sum()    // 7.2

To sum a property of a custom object we can extend Sequence to take a keypath with a generic value that conforms to AdditiveArithmetic as parameter:

extension Sequence  {
    func sum(_ keyPath: KeyPath) -> T { reduce(.zero) { $0 + $1[keyPath: keyPath] } }
}

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Usage:

struct Product {
    let id: String
    let price: Decimal
}

let products: [Product] = [.init(id: "abc", price: 21.9),
                           .init(id: "xyz", price: 19.7),
                           .init(id: "jkl", price: 2.9)
]

products.sum(\.price)  // 44.5