Extension random() to select random element from a collection

Fixes #KT-15539

libraries/stdlib/common/src/generated/_Arrays.kt

@@ -16,6 +16,7 @@ package kotlin.collections
 import kotlin.*
 import kotlin.text.*
 import kotlin.comparisons.*
+import kotlin.random.*
 
 /**
  * Returns 1st *element* from the collection.
@@ -2049,6 +2050,213 @@ public inline fun CharArray.lastOrNull(predicate: (Char) -> Boolean): Char? {
     return null
 }
 
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun <T> Array<out T>.random(): T {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun ByteArray.random(): Byte {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun ShortArray.random(): Short {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun IntArray.random(): Int {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun LongArray.random(): Long {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun FloatArray.random(): Float {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun DoubleArray.random(): Double {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun BooleanArray.random(): Boolean {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun CharArray.random(): Char {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+public fun <T> Array<out T>.random(random: Random): T {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+public fun ByteArray.random(random: Random): Byte {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+public fun ShortArray.random(random: Random): Short {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+public fun IntArray.random(random: Random): Int {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+public fun LongArray.random(random: Random): Long {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+public fun FloatArray.random(random: Random): Float {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+public fun DoubleArray.random(random: Random): Double {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+public fun BooleanArray.random(random: Random): Boolean {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+public fun CharArray.random(random: Random): Char {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
 /**
  * Returns the single element, or throws an exception if the array is empty or has more than one element.
  */

libraries/stdlib/common/src/generated/_Collections.kt

@@ -16,6 +16,7 @@ package kotlin.collections
 import kotlin.*
 import kotlin.text.*
 import kotlin.comparisons.*
+import kotlin.random.*
 
 /**
  * Returns 1st *element* from the collection.
@@ -456,6 +457,29 @@ public inline fun <T> List<T>.lastOrNull(predicate: (T) -> Boolean): T? {
     return null
 }
 
+/**
+ * Returns a random element from this collection.
+ * 
+ * @throws NoSuchElementException if this collection is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun <T> Collection<T>.random(): T {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this collection using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this collection is empty.
+ */
+@SinceKotlin("1.3")
+public fun <T> Collection<T>.random(random: Random): T {
+    if (isEmpty())
+        throw NoSuchElementException("Collection is empty.")
+    return elementAt(random.nextInt(size))
+}
+
 /**
  * Returns the single element, or throws an exception if the collection is empty or has more than one element.
  */

libraries/stdlib/common/src/generated/_Comparisons.kt

@@ -16,6 +16,7 @@ package kotlin.comparisons
 import kotlin.*
 import kotlin.text.*
 import kotlin.comparisons.*
+import kotlin.random.*
 
 /**
  * Returns the greater of two values.

libraries/stdlib/common/src/generated/_Maps.kt

@@ -16,6 +16,7 @@ package kotlin.collections
 import kotlin.*
 import kotlin.text.*
 import kotlin.comparisons.*
+import kotlin.random.*
 
 /**
  * Returns a [List] containing all key-value pairs.

libraries/stdlib/common/src/generated/_Ranges.kt

@@ -16,6 +16,70 @@ package kotlin.ranges
 import kotlin.*
 import kotlin.text.*
 import kotlin.comparisons.*
+import kotlin.random.*
+
+/**
+ * Returns a random element from this range.
+ * 
+ * @throws IllegalArgumentException if this range is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun IntRange.random(): Int {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this range.
+ * 
+ * @throws IllegalArgumentException if this range is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun LongRange.random(): Long {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this range.
+ * 
+ * @throws IllegalArgumentException if this range is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun CharRange.random(): Char {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this range using the specified source of randomness.
+ * 
+ * @throws IllegalArgumentException if this range is empty.
+ */
+@SinceKotlin("1.3")
+public fun IntRange.random(random: Random): Int {
+    return random.nextInt(this)
+}
+
+/**
+ * Returns a random element from this range using the specified source of randomness.
+ * 
+ * @throws IllegalArgumentException if this range is empty.
+ */
+@SinceKotlin("1.3")
+public fun LongRange.random(random: Random): Long {
+    return random.nextLong(this)
+}
+
+/**
+ * Returns a random element from this range using the specified source of randomness.
+ * 
+ * @throws IllegalArgumentException if this range is empty.
+ */
+@SinceKotlin("1.3")
+public fun CharRange.random(random: Random): Char {
+    return random.nextInt(first.toInt(), last.toInt() + 1).toChar()
+}
 
 /**
  * Checks if the specified [value] belongs to this range.

libraries/stdlib/common/src/generated/_Sequences.kt

@@ -16,6 +16,7 @@ package kotlin.sequences
 import kotlin.*
 import kotlin.text.*
 import kotlin.comparisons.*
+import kotlin.random.*
 import kotlin.coroutines.experimental.*
 
 /**

libraries/stdlib/common/src/generated/_Sets.kt

@@ -16,6 +16,7 @@ package kotlin.collections
 import kotlin.*
 import kotlin.text.*
 import kotlin.comparisons.*
+import kotlin.random.*
 
 /**
  * Returns a set containing all elements of the original set except the given [element].

libraries/stdlib/common/src/generated/_Strings.kt

@@ -16,6 +16,7 @@ package kotlin.text
 import kotlin.*
 import kotlin.text.*
 import kotlin.comparisons.*
+import kotlin.random.*
 
 /**
  * Returns a character at the given [index] or throws an [IndexOutOfBoundsException] if the [index] is out of bounds of this char sequence.
@@ -170,6 +171,29 @@ public inline fun CharSequence.lastOrNull(predicate: (Char) -> Boolean): Char? {
     return null
 }
 
+/**
+ * Returns a random character from this char sequence.
+ * 
+ * @throws NoSuchElementException if this char sequence is empty.
+ */
+@SinceKotlin("1.3")
+@kotlin.internal.InlineOnly
+public inline fun CharSequence.random(): Char {
+    return random(Random)
+}
+
+/**
+ * Returns a random character from this char sequence using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this char sequence is empty.
+ */
+@SinceKotlin("1.3")
+public fun CharSequence.random(random: Random): Char {
+    if (isEmpty())
+        throw NoSuchElementException("Char sequence is empty.")
+    return get(random.nextInt(length))
+}
+
 /**
  * Returns the single character, or throws an exception if the char sequence is empty or has more than one character.
  */

libraries/stdlib/common/src/generated/_UArrays.kt

@@ -16,6 +16,107 @@ package kotlin.collections
 import kotlin.*
 import kotlin.text.*
 import kotlin.comparisons.*
+import kotlin.random.*
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+@kotlin.internal.InlineOnly
+public inline fun UIntArray.random(): UInt {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+@kotlin.internal.InlineOnly
+public inline fun ULongArray.random(): ULong {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+@kotlin.internal.InlineOnly
+public inline fun UByteArray.random(): UByte {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+@kotlin.internal.InlineOnly
+public inline fun UShortArray.random(): UShort {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+public fun UIntArray.random(random: Random): UInt {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+public fun ULongArray.random(random: Random): ULong {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+public fun UByteArray.random(random: Random): UByte {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
+
+/**
+ * Returns a random element from this array using the specified source of randomness.
+ * 
+ * @throws NoSuchElementException if this array is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+public fun UShortArray.random(random: Random): UShort {
+    if (isEmpty())
+        throw NoSuchElementException("Array is empty.")
+    return get(random.nextInt(size))
+}
 
 /**
  * Returns an array of type [ByteArray], which is a view of this array where each element is a signed reinterpretation

libraries/stdlib/common/src/generated/_URanges.kt

@@ -16,6 +16,53 @@ package kotlin.ranges
 import kotlin.*
 import kotlin.text.*
 import kotlin.comparisons.*
+import kotlin.random.*
+
+/**
+ * Returns a random element from this range.
+ * 
+ * @throws IllegalArgumentException if this range is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+@kotlin.internal.InlineOnly
+public inline fun UIntRange.random(): UInt {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this range.
+ * 
+ * @throws IllegalArgumentException if this range is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+@kotlin.internal.InlineOnly
+public inline fun ULongRange.random(): ULong {
+    return random(Random)
+}
+
+/**
+ * Returns a random element from this range using the specified source of randomness.
+ * 
+ * @throws IllegalArgumentException if this range is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+public fun UIntRange.random(random: Random): UInt {
+    return random.nextUInt(this)
+}
+
+/**
+ * Returns a random element from this range using the specified source of randomness.
+ * 
+ * @throws IllegalArgumentException if this range is empty.
+ */
+@SinceKotlin("1.3")
+@ExperimentalUnsignedTypes
+public fun ULongRange.random(random: Random): ULong {
+    return random.nextULong(this)
+}
 
 /**
  * Returns a progression from this value down to the specified [to] value with the step -1.

libraries/stdlib/test/collections/ArraysTest.kt

@@ -11,6 +11,7 @@ import test.collections.behaviors.*
 import test.comparisons.STRING_CASE_INSENSITIVE_ORDER
 import kotlin.test.*
 import kotlin.comparisons.*
+import kotlin.random.Random
 
 fun <T> assertArrayNotSameButEquals(expected: Array<out T>, actual: Array<out T>, message: String = "") { assertTrue(expected !== actual && expected contentEquals actual, message) }
 fun assertArrayNotSameButEquals(expected: IntArray, actual: IntArray, message: String = "") {             assertTrue(expected !== actual && expected contentEquals actual, message) }
@@ -592,6 +593,31 @@ class ArraysTest {
         expect(2) { arrayOf(1, 2, 3).last { it % 2 == 0 } }
     }
 
+
+    @Test fun random() {
+        Array(100) { it }.let { array ->
+            val tosses = List(10) { array.random() }
+            assertTrue(tosses.distinct().size > 1, "Should be some distinct elements in $tosses")
+
+            val seed = Random.nextInt()
+            val random1 = Random(seed)
+            val random2 = Random(seed)
+
+            val tosses1 = List(10) { array.random(random1) }
+            val tosses2 = List(10) { array.random(random2) }
+
+            assertEquals(tosses1, tosses2)
+        }
+
+        arrayOf("x").let { singletonArray ->
+            val tosses = List(10) { singletonArray.random() }
+            assertEquals(singletonArray.toList(), tosses.distinct())
+        }
+
+        assertFailsWith<NoSuchElementException> { emptyArray<Any>().random() }
+    }
+
+
     @Test fun contains() {
         assertTrue(arrayOf("1", "2", "3", "4").contains("2"))
         assertTrue("3" in arrayOf("1", "2", "3", "4"))

libraries/stdlib/test/collections/CollectionTest.kt

@@ -10,6 +10,8 @@ import kotlin.test.*
 import test.collections.behaviors.*
 import test.comparisons.STRING_CASE_INSENSITIVE_ORDER
 import kotlin.comparisons.*
+import kotlin.math.sin
+import kotlin.random.Random
 
 class CollectionTest {
 
@@ -620,6 +622,31 @@ class CollectionTest {
         assertFails { arrayListOf<Int>().last() }
     }
 
+    @Test fun random() {
+        val list = List(100) { it }
+        val set = list.toSet()
+        listOf(list, set).forEach { collection: Collection<Int> ->
+            val tosses = List(10) { collection.random() }
+            assertTrue(tosses.distinct().size > 1, "Should be some distinct elements in $tosses")
+
+            val seed = Random.nextInt()
+            val random1 = Random(seed)
+            val random2 = Random(seed)
+
+            val tosses1 = List(10) { collection.random(random1) }
+            val tosses2 = List(10) { collection.random(random2) }
+
+            assertEquals(tosses1, tosses2)
+        }
+
+        listOf("x").let { singletonList ->
+            val tosses = List(10) { singletonList.random() }
+            assertEquals(singletonList, tosses.distinct())
+        }
+
+        assertFailsWith<NoSuchElementException> { emptyList<Any>().random() }
+    }
+
     @Test fun subscript() {
         val list = arrayListOf("foo", "bar")
         assertEquals("foo", list[0])

libraries/stdlib/test/text/StringTest.kt

@@ -10,6 +10,7 @@ import test.*
 import test.collections.behaviors.iteratorBehavior
 import test.collections.compare
 import kotlin.math.sign
+import kotlin.random.Random
 
 
 fun createString(content: String): CharSequence = content
@@ -936,6 +937,29 @@ class StringTest {
         assertNull(data.filterNot { it.isAsciiLetter() || it.isAsciiDigit() }.firstOrNull())
     }
 
+    @Test fun random() = withOneCharSequenceArg { data ->
+        data("abcdefg").let { charSeq ->
+            val tosses = List(10) { charSeq.random() }
+            assertTrue(tosses.distinct().size > 1, "Should be some distinct elements in $tosses")
+
+            val seed = Random.nextInt()
+            val random1 = Random(seed)
+            val random2 = Random(seed)
+
+            val tosses1 = List(10) { charSeq.random(random1) }
+            val tosses2 = List(10) { charSeq.random(random2) }
+
+            assertEquals(tosses1, tosses2)
+        }
+
+        data("x").let { singletonCharSeq ->
+            val tosses = List(10) { singletonCharSeq.random() }
+            assertEquals(singletonCharSeq.toList(), tosses.distinct())
+        }
+
+        assertFailsWith<NoSuchElementException> { data("").random() }
+    }
+
     @Test fun partition() {
         val data = "a1b2c3"
         val pair = data.partition { it.isAsciiDigit() }