Swift: Ways to Calculate the Product of an Array

The product of an array in Swift (and other programming languages) is the result of multiplying all the elements of the array together. For example, the product of [2, 3, 4] is 2 * 3 * 4 = 24. This practical, code-centric article will walk you through 3 different ways to calculate the product of a given array in Swift.

Using a for loop

You can use a for loop to iterate over the array and update a variable that stores the current product:

let array = [2, 3, 4, 5, 9, 10, 11, 12, 13, 14, 15]
var product = 1
for number in array {
    product *= number
}

print(product)

Output:

3891888000

Using the reduce() method

The reduce() method of the Array class takes an initial value and a closure that combines each element of the array with the previous result and returns the final result. In the context of this tutorial, you can use it like so:

let array = [2, 3, 4, 8, 9, 10, 11, 12, 13]
let product = array.reduce(1) { $0 * $1 }
print(product)

Output:

29652480

Using the map() and joined(separator:) methods

What we will do is to use the map() and the joined(separator:) methods of the Array class to convert each element of the input array to a string, then join them with a multiplication sign as a separator and evaluates the resulting expression using NSExpression.

Example:

import Foundation

let array = [2, 3, 4, 5, 6]
let expression = array.map(String.init).joined(separator: "*")

let product = NSExpression(
    format: expression).expressionValue(with: nil, context: nil) as! Int
print(product)

Output:

720

I put this approach here just for your reference. It is not very efficient or elegant. It involves converting each element of the array to a string, concatenating them with a multiplication sign, and then parsing and evaluating the resulting expression using NSExpression. This makes a lot of unnecessary string manipulation and computation that can be avoided by using other solutions.