Using the 'flatMap' Function for Transforming Nested Collections

The 'flatMap' function is a powerful tool in Kotlin for transforming collections that contain nested structures. It allows you to map each element of a collection to a collection itself and then flatten the resulting collections into a single collection. This is particularly useful when dealing with lists of lists or when you need to extract multiple elements from each item in a collection.

val listOfLists = listOf(
    listOf(1, 2, 3),
    listOf(4, 5),
    listOf(6, 7, 8, 9)
)

val flattenedList = listOfLists.flatMap { it }

// Result: [1, 2, 3, 4, 5, 6, 7, 8, 9]