Can you explain the difference between flatMap and compactMap in programming languages?

In programming languages like Swift, flatMap and compactMap are used for transforming collections but serve different purposes:

• flatMap is used to transform elements of a collection into collections and then "flatten" (flat) the result into a single level. For example, if each element is transformed into an array, flatMap will combine all these arrays into one.

• compactMap transforms the elements of a collection while simultaneously discarding all nil (or missing) values. This is useful when the transformation may return an optional value, and you want to get an array with only non-empty results.

Example in Swift:

let numbers = ["1", "2", "three", "4"]

// compactMap converts strings to Int, discarding non-numeric
let ints = numbers.compactMap { Int($0) } // [1, 2, 4]

// flatMap with arrays
let nested = [[1, 2], [3, 4], [5]]
let flat = nested.flatMap { $0 } // [1, 2, 3, 4, 5]

Thus, compactMap filters and transforms, while flatMap combines nested collections after transformation.