Provide unzip method for Iterables, Arrays and Sequences of pairs.

#KT-5793 Fixed

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

@@ -32,3 +32,48 @@ public fun <T> Array<Array<out T>>.flatten(): List<T> {
     return result
 }
 
+/**
+ * Returns a pair of lists, where
+ * *first* list is built from the first values of each pair from this collection,
+ * *second* list is built from the second values of each pair from this collection.
+ */
+public fun <T, R> Iterable<Pair<T, R>>.unzip(): Pair<List<T>, List<R>> {
+    val expectedSize = collectionSizeOrDefault(10)
+    val listT = ArrayList<T>(expectedSize)
+    val listR = ArrayList<R>(expectedSize)
+    for (pair in this) {
+        listT.add(pair.first)
+        listR.add(pair.second)
+    }
+    return listT to listR
+}
+
+/**
+ * Returns a pair of lists, where
+ * *first* list is built from the first values of each pair from this array,
+ * *second* list is built from the second values of each pair from this array.
+ */
+public fun <T, R> Array<Pair<T, R>>.unzip(): Pair<List<T>, List<R>> {
+    val listT = ArrayList<T>(size())
+    val listR = ArrayList<R>(size())
+    for (pair in this) {
+        listT.add(pair.first)
+        listR.add(pair.second)
+    }
+    return listT to listR
+}
+
+/**
+ * Returns a pair of lists, where
+ * *first* list is built from the first values of each pair from this sequence,
+ * *second* list is built from the second values of each pair from this sequence.
+ */
+public fun <T, R> Sequence<Pair<T, R>>.unzip(): Pair<List<T>, List<R>> {
+    val listT = ArrayList<T>()
+    val listR = ArrayList<R>()
+    for (pair in this) {
+        listT.add(pair.first)
+        listR.add(pair.second)
+    }
+    return listT to listR
+}

libraries/stdlib/test/collections/CollectionTest.kt

@@ -621,6 +621,19 @@ class CollectionTest {
         assertEquals(e, 5)
     }
 
+    test fun unzipList() {
+        val list = listOf(1 to 'a', 2 to 'b', 3 to 'c')
+        val (ints, chars) = list.unzip()
+        assertEquals(listOf(1, 2, 3), ints)
+        assertEquals(listOf('a', 'b', 'c'), chars)
+    }
+
+    test fun unzipArray() {
+        val array = arrayOf(1 to 'a', 2 to 'b', 3 to 'c')
+        val (ints, chars) = array.unzip()
+        assertEquals(listOf(1, 2, 3), ints)
+        assertEquals(listOf('a', 'b', 'c'), chars)
+    }
 
     test fun specialLists() {
         compare(arrayListOf<Int>(), listOf<Int>()) { listBehavior() }

libraries/stdlib/test/collections/SequenceTest.kt

@@ -291,8 +291,7 @@ public class SequenceTest {
         assertEquals(listOf(0, 1, 3, 4), result.toList())
     }
 
-    test
+    test fun flatten() {
-    fun flatten() {
         val data = sequenceOf(1, 2).map { sequenceOf(0..it) }
         assertEquals(listOf(0, 1, 0, 1, 2), data.flatten().toList())
     }
@@ -307,6 +306,12 @@ public class SequenceTest {
         assertEquals(listOf(13, 34, 55, 144), sequence.distinctBy { it % 4 }.toList())
     }
 
+    test fun unzip() {
+        val seq = sequenceOf(1 to 'a', 2 to 'b', 3 to 'c')
+        val (ints, chars) = seq.unzip()
+        assertEquals(listOf(1, 2, 3), ints)
+        assertEquals(listOf('a', 'b', 'c'), chars)
+    }
 
     /*
     test fun pairIterator() {