CODEWITHSUNDEEP
arraysswiftsumreduce
Womble Tristes
Womble Tristes

Reputation: 443

Sum of Array containing custom class (Swift)

i am figuring out a way to get the sum of values of classes which are contained in an array. My setup is as follows:

class CustomClass {
    var value: Int?
    init(value: Int) {
       self.value = value
    }
}

let object1 = CustomClass(value: 2)
let object2 = CustomClass(value: 4)
let object3 = CustomClass(value: 8)

let array: [CustomClass] = [object1, object2, object3]

My current solution is as follows:

var sumArray = [Int]()
for object in array {
    sumArray.append(object.value!)
}
let sum = sumArray.reduce(0, +)

The problem is that it gets very complex with classes with many other values, does anybody know a better solution?

Upvotes: 5

Views: 5146

Answers (4)

Pepe Ruiz
Pepe Ruiz

Reputation: 1

Short way:

let sum = customArray.reduce(0) { $0 + $1.intValue }

Upvotes: 0

Leo Dabus
Leo Dabus

Reputation: 236360

I would create a protocol for your class or structures that contains a value. And change its declaration to non optional.

protocol Valueable {
    var value: Int { get }
}

Then you will need to make your class conform to that protocol:

class CustomClass: Valueable {
    let value: Int
    init(value: Int) {
        self.value = value
    }
}

Now you can extend the collection protocol with a read only instance property to return the sum of all elements in your array.

extension Collection where Element: Valueable {
    var sum: Int {
        return reduce(0) { $0 + $1.value }
    }
} 

let object1 = CustomClass(value: 2)
let object2 = CustomClass(value: 4)
let object3 = CustomClass(value: 8)

let objects = [object1, object2, object3]

let sum = objects.sum   // 14

edit/update:

Another option is to extend sequence and add a generic sum method that accepts a key path that its property conforms to AdditiveArithmetic

or add an associated type to the protocol that conforms to AdditiveArithmetic:

protocol Valueable {
    associatedtype Value: AdditiveArithmetic
    var value: Value { get }
}

extension Collection where Element: Valueable {
    var sum: Element.Value { reduce(.zero) { $0 + $1.value } }
}

class CustomClass: Valueable {
    let value: Decimal
    init(value: Decimal) {
        self.value = value
    }
}

Usage:

let object1 = CustomClass(value: 123.4567)
let object2 = CustomClass(value: 12.34567)
let object3 = CustomClass(value: 1.234567)

let objects = [object1, object2, object3]

let sum = objects.sum   // 137.036937

Upvotes: 1

sarawanak
sarawanak

Reputation: 439

You can compactMap your array of custom class into array of integer and then reduce that array to its sum. Like,

let sum = array.lazy.compactMap { $0.value }
            .reduce(0, +)

Upvotes: 13

David Pasztor
David Pasztor

Reputation: 54716

You can use a single reduce on array.

let sumOfValues = array.reduce({$0 += ($1.value ?? 0)})

Upvotes: 3

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