Finding sum of elements in Swift array

Swift3 has changed to :

let multiples = [...]
sum = multiples.reduce(0, +)

Swift 3+ one liner to sum properties of objects

var totalSum = scaleData.map({$0.points}).reduce(0, +)

Where points is the property in my custom object scaleData that I am trying to reduce

This is the easiest/shortest method I can find.

Swift 3 and Swift 4:

let multiples = [...]
let sum = multiples.reduce(0, +)
print("Sum of Array is : ", sum)

Swift 2:

let multiples = [...]
sum = multiples.reduce(0, combine: +)

---

Some more info:

This uses Array's reduce method (documentation here), which allows you to "reduce a collection of elements down to a single value by recursively applying the provided closure". We give it 0 as the initial value, and then, essentially, the closure { $0 + $1 }. Of course, we can simplify that to a single plus sign, because that's how Swift rolls.

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, +) }
}

---

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, +)
    }
}

---

Xcode 11 • Swift 5.1 or later

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

---

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 predicate to return a value that conforms to AdditiveArithmetic:

extension Sequence  {
    func sum<T: AdditiveArithmetic>(_ predicate: (Element) -> T) -> T { reduce(.zero) { $0 + predicate($1) } }
}

---

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