Swift has a built-in higher-order function named map that can be used with collection types such as arrays. The map function solves the problem of transforming the elements of an array using a function. The following example presents two different approaches to transform a set of numbers:
let numbers = [10, 30, 91, 50, 100, 39, 74] var formattedNumbers: [String] = [] for number in numbers { let formattedNumber = "\(number)$" formattedNumbers.append(formattedNumber) } let mappedNumbers = numbers.map { "\($0)$" }
The first approach to solve the problem is imperative and uses a for-in loop to go through the collection and transform each element in the array. This iteration technique is known as external iteration because ...
