groupBy
Groups elements of the original sequence by the key returned by the given keySelector function applied to each element and returns a map where each group key is associated with a list of corresponding elements.
inline fun <T, K> Sequence<T>.groupBy(keySelector: (T) -> K): Map<K, List<T>>(source)
val words = sequenceOf("apple", "banana", "cherry", "date")
val groupedByLength = words.groupBy { it.length }
println(groupedByLength) // Output: {5=[apple], 6=[banana, cherry], 4=[date]}