CompactMap vs FlatMap — Swift

Map

Map is a function in Swift that takes an array and applies a given closure (a block of code) to each element of the array, returning a new array containing the results. The closure is passed each element of the original array one at a time, and the closure's return value is used to create a new element in the resulting array.

let numbers = [1, 2, 3, 4]
let squaredNumbers = numbers.map { $0 * $0 }
print(squaredNumbers)  // [1, 4, 9, 16]

In this example, the map function is called on the numbers array and it applies the closure {$0 * $0} to each element of the array and returns new array with the squared values of the original array

let stringArray = ["1", "2", "3"]
let intArray = stringArray.map { Int($0) }
print(intArray)  // [1, 2, 3]

In this example, the map function is called on the stringArray and it applies the closure {Int($0)} to each element of the array and returns new array with the int values of the original array.

CompactMap

compactMap is similar to map, but it also filters out any nil values that may be produced by the closure, and returns a new array containing the non-nil results.

let array: [Int?] = [1, nil, 2, nil, 3]
let compactedArray = array.compactMap { $0 }
print(compactedArray) // [1, 2, 3]

FlatMap

flatMap is also similar to map, but instead of returning an array of arrays, it returns a single array containing all of the elements from the inner arrays.

let arrayOfArrays = [[1, 2, 3], [4, 5], [6]]
let flattenedArray = arrayOfArrays.flatMap { $0 }
print(flattenedArray) // [1, 2, 3, 4, 5, 6]