flatten

Returns a sequence of all elements from all sequences in this sequence.

fun <T> Sequence<Sequence<T>>.flatten(): Sequence<T>(source)

val nested = sequenceOf(
    sequenceOf("a", "b"),
    sequenceOf("c"),
    sequenceOf("d", "e", "f")
)

val flattened: Sequence<String> = nested.flatten()

println(flattened.toList())  // prints: [a, b, c, d, e, f]

Source