Add samples for flatten, unzip functions

libraries/stdlib/samples/test/samples/collections/sequences.kt

@@ -242,6 +242,32 @@ class Sequences {
             assertPrints(even, "[0, 2, 8, 34]")
             assertPrints(odd, "[1, 1, 3, 5, 13, 21]")
         }
+
+        @Sample
+        fun flattenSequenceOfSequences() {
+            val sequence: Sequence<Int> = generateSequence(1) { it + 1 }
+            val sequenceOfSequences: Sequence<Sequence<Int>> = sequence.map { number ->
+                generateSequence { number }.take(number)
+            }
+
+            assertPrints(sequenceOfSequences.flatten().take(10).toList(), "[1, 2, 2, 3, 3, 3, 4, 4, 4, 4]")
+        }
+
+        @Sample
+        fun flattenSequenceOfLists() {
+            val sequence: Sequence<String> = sequenceOf("123", "45")
+            val sequenceOfLists: Sequence<List<Char>> = sequence.map { it.toList() }
+
+            assertPrints(sequenceOfLists.flatten().toList(), "[1, 2, 3, 4, 5]")
+        }
+
+        @Sample
+        fun unzip() {
+            val result = generateSequence(0 to 1) { it.first + 1 to it.second * 2 }.take(8).unzip()
+
+            assertPrints(result.first.toList(), "[0, 1, 2, 3, 4, 5, 6, 7]")
+            assertPrints(result.second.toList(), "[1, 2, 4, 8, 16, 32, 64, 128]")
+        }
     }
 
 }

libraries/stdlib/src/kotlin/collections/Sequences.kt

@@ -76,6 +76,8 @@ public fun <T> Sequence<T>.ifEmpty(defaultValue: () -> Sequence<T>): Sequence<T>
  * Returns a sequence of all elements from all sequences in this sequence.
  *
  * The operation is _intermediate_ and _stateless_.
+ *
+ * @sample samples.collections.Sequences.Transformations.flattenSequenceOfSequences
  */
 public fun <T> Sequence<Sequence<T>>.flatten(): Sequence<T> = flatten { it.iterator() }
 
@@ -83,6 +85,8 @@ public fun <T> Sequence<Sequence<T>>.flatten(): Sequence<T> = flatten { it.itera
  * Returns a sequence of all elements from all iterables in this sequence.
  *
  * The operation is _intermediate_ and _stateless_.
+ *
+ * @sample samples.collections.Sequences.Transformations.flattenSequenceOfLists
  */
 @kotlin.jvm.JvmName("flattenSequenceOfIterable")
 public fun <T> Sequence<Iterable<T>>.flatten(): Sequence<T> = flatten { it.iterator() }
@@ -100,6 +104,8 @@ private fun <T, R> Sequence<T>.flatten(iterator: (T) -> Iterator<R>): Sequence<R
  * *second* list is built from the second values of each pair from this sequence.
  *
  * The operation is _terminal_.
+ *
+ * @sample samples.collections.Sequences.Transformations.unzip
  */
 public fun <T, R> Sequence<Pair<T, R>>.unzip(): Pair<List<T>, List<R>> {
     val listT = ArrayList<T>()