Explain the working principle of the Flat Map method and how it differs from the regular Map when processing data collections.

The map method transforms each element of a collection by applying a function and returns an array of the results. If the function returns a collection, the result will be an array of collections.

flatMap first applies the function to each element like map, but then "flattens" (flattens) the nested collections into a single flat array.

Example:

let numbers = [1, 2, 3]

// map with a function returning an array
let mapped = numbers.map { Array(repeating: $0, count: $0) }
// mapped = [[1], [2, 2], [3, 3, 3]]

// flatMap with the same function
let flatMapped = numbers.flatMap { Array(repeating: $0, count: $0) }
// flatMapped = [1, 2, 2, 3, 3, 3]

Thus, flatMap is useful when the function returns a collection and you want to obtain a single flat array without nested arrays.