standard library: 'maxBy' and 'minBy' functions added (#KT-4267 fixed)

libraries/stdlib/src/generated/_Arrays.kt

@@ -239,6 +239,25 @@ public fun <T: Comparable<T>> Array<out T>.max() : T? {
     return max
 }
 
+/**
+ * Returns the first element yielding the largest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>, T: Any> Array<out T>.maxBy(f: (T) -> R) : T? {
+    if (isEmpty()) return null
+    
+    var maxElem = this[0]
+    var maxValue = f(maxElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (maxValue < v) {
+           maxElem = e
+           maxValue = v
+        }
+    }
+    return maxElem
+}
+
 /**
  * Returns the smallest element or null if there are no elements
  */
@@ -252,6 +271,25 @@ public fun <T: Comparable<T>> Array<out T>.min() : T? {
     return min
 }
 
+/**
+ * Returns the first element yielding the smallest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>, T: Any> Array<out T>.minBy(f: (T) -> R) : T? {
+    if (size == 0) return null
+    
+    var minElem = this[0]
+    var minValue = f(minElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (minValue > v) {
+           minElem = e
+           minValue = v
+        }
+    }
+    return minElem
+}
+
 /**
  * Partitions this collection into a pair of collections
  */

libraries/stdlib/src/generated/_BooleanArrays.kt

@@ -225,6 +225,44 @@ public inline fun <R, C: MutableCollection<in R>> BooleanArray.mapTo(result: C,
     return result
 }
 
+/**
+ * Returns the first element yielding the largest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> BooleanArray.maxBy(f: (Boolean) -> R) : Boolean? {
+    if (isEmpty()) return null
+    
+    var maxElem = this[0]
+    var maxValue = f(maxElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (maxValue < v) {
+           maxElem = e
+           maxValue = v
+        }
+    }
+    return maxElem
+}
+
+/**
+ * Returns the first element yielding the smallest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> BooleanArray.minBy(f: (Boolean) -> R) : Boolean? {
+    if (size == 0) return null
+    
+    var minElem = this[0]
+    var minValue = f(minElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (minValue > v) {
+           minElem = e
+           minValue = v
+        }
+    }
+    return minElem
+}
+
 /**
  * Partitions this collection into a pair of collections
  */

libraries/stdlib/src/generated/_ByteArrays.kt

@@ -238,6 +238,25 @@ public fun ByteArray.max() : Byte? {
     return max
 }
 
+/**
+ * Returns the first element yielding the largest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> ByteArray.maxBy(f: (Byte) -> R) : Byte? {
+    if (isEmpty()) return null
+    
+    var maxElem = this[0]
+    var maxValue = f(maxElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (maxValue < v) {
+           maxElem = e
+           maxValue = v
+        }
+    }
+    return maxElem
+}
+
 /**
  * Returns the smallest element or null if there are no elements
  */
@@ -251,6 +270,25 @@ public fun ByteArray.min() : Byte? {
     return min
 }
 
+/**
+ * Returns the first element yielding the smallest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> ByteArray.minBy(f: (Byte) -> R) : Byte? {
+    if (size == 0) return null
+    
+    var minElem = this[0]
+    var minValue = f(minElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (minValue > v) {
+           minElem = e
+           minValue = v
+        }
+    }
+    return minElem
+}
+
 /**
  * Partitions this collection into a pair of collections
  */

libraries/stdlib/src/generated/_CharArrays.kt

@@ -225,6 +225,44 @@ public inline fun <R, C: MutableCollection<in R>> CharArray.mapTo(result: C, tra
     return result
 }
 
+/**
+ * Returns the first element yielding the largest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> CharArray.maxBy(f: (Char) -> R) : Char? {
+    if (isEmpty()) return null
+    
+    var maxElem = this[0]
+    var maxValue = f(maxElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (maxValue < v) {
+           maxElem = e
+           maxValue = v
+        }
+    }
+    return maxElem
+}
+
+/**
+ * Returns the first element yielding the smallest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> CharArray.minBy(f: (Char) -> R) : Char? {
+    if (size == 0) return null
+    
+    var minElem = this[0]
+    var minValue = f(minElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (minValue > v) {
+           minElem = e
+           minValue = v
+        }
+    }
+    return minElem
+}
+
 /**
  * Partitions this collection into a pair of collections
  */

libraries/stdlib/src/generated/_DoubleArrays.kt

@@ -238,6 +238,25 @@ public fun DoubleArray.max() : Double? {
     return max
 }
 
+/**
+ * Returns the first element yielding the largest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> DoubleArray.maxBy(f: (Double) -> R) : Double? {
+    if (isEmpty()) return null
+    
+    var maxElem = this[0]
+    var maxValue = f(maxElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (maxValue < v) {
+           maxElem = e
+           maxValue = v
+        }
+    }
+    return maxElem
+}
+
 /**
  * Returns the smallest element or null if there are no elements
  */
@@ -251,6 +270,25 @@ public fun DoubleArray.min() : Double? {
     return min
 }
 
+/**
+ * Returns the first element yielding the smallest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> DoubleArray.minBy(f: (Double) -> R) : Double? {
+    if (size == 0) return null
+    
+    var minElem = this[0]
+    var minValue = f(minElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (minValue > v) {
+           minElem = e
+           minValue = v
+        }
+    }
+    return minElem
+}
+
 /**
  * Partitions this collection into a pair of collections
  */

libraries/stdlib/src/generated/_FloatArrays.kt

@@ -238,6 +238,25 @@ public fun FloatArray.max() : Float? {
     return max
 }
 
+/**
+ * Returns the first element yielding the largest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> FloatArray.maxBy(f: (Float) -> R) : Float? {
+    if (isEmpty()) return null
+    
+    var maxElem = this[0]
+    var maxValue = f(maxElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (maxValue < v) {
+           maxElem = e
+           maxValue = v
+        }
+    }
+    return maxElem
+}
+
 /**
  * Returns the smallest element or null if there are no elements
  */
@@ -251,6 +270,25 @@ public fun FloatArray.min() : Float? {
     return min
 }
 
+/**
+ * Returns the first element yielding the smallest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> FloatArray.minBy(f: (Float) -> R) : Float? {
+    if (size == 0) return null
+    
+    var minElem = this[0]
+    var minValue = f(minElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (minValue > v) {
+           minElem = e
+           minValue = v
+        }
+    }
+    return minElem
+}
+
 /**
  * Partitions this collection into a pair of collections
  */

libraries/stdlib/src/generated/_IntArrays.kt

@@ -238,6 +238,25 @@ public fun IntArray.max() : Int? {
     return max
 }
 
+/**
+ * Returns the first element yielding the largest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> IntArray.maxBy(f: (Int) -> R) : Int? {
+    if (isEmpty()) return null
+    
+    var maxElem = this[0]
+    var maxValue = f(maxElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (maxValue < v) {
+           maxElem = e
+           maxValue = v
+        }
+    }
+    return maxElem
+}
+
 /**
  * Returns the smallest element or null if there are no elements
  */
@@ -251,6 +270,25 @@ public fun IntArray.min() : Int? {
     return min
 }
 
+/**
+ * Returns the first element yielding the smallest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> IntArray.minBy(f: (Int) -> R) : Int? {
+    if (size == 0) return null
+    
+    var minElem = this[0]
+    var minValue = f(minElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (minValue > v) {
+           minElem = e
+           minValue = v
+        }
+    }
+    return minElem
+}
+
 /**
  * Partitions this collection into a pair of collections
  */

libraries/stdlib/src/generated/_Iterables.kt

@@ -225,6 +225,26 @@ public fun <T: Comparable<T>> Iterable<T>.max() : T? {
     return max
 }
 
+/**
+ * Returns the first element yielding the largest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>, T: Any> Iterable<T>.maxBy(f: (T) -> R) : T? {
+    val iterator = iterator()
+    if (!iterator.hasNext()) return null
+    
+    var maxElem = iterator.next()
+    var maxValue = f(maxElem)
+    while (iterator.hasNext()) {
+        val e = iterator.next()
+        val v = f(e)
+        if (maxValue < v) {
+           maxElem = e
+           maxValue = v
+        }
+    }
+    return maxElem
+}
+
 /**
  * Returns the smallest element or null if there are no elements
  */
@@ -238,6 +258,26 @@ public fun <T: Comparable<T>> Iterable<T>.min() : T? {
     return min
 }
 
+/**
+ * Returns the first element yielding the smallest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>, T: Any> Iterable<T>.minBy(f: (T) -> R) : T? {
+    val iterator = iterator()
+    if (!iterator.hasNext()) return null
+    
+    var minElem = iterator.next()
+    var minValue = f(minElem)
+    while (iterator.hasNext()) {
+        val e = iterator.next()
+        val v = f(e)
+        if (minValue > v) {
+           minElem = e
+           minValue = v
+        }
+    }
+    return minElem
+}
+
 /**
  * Partitions this collection into a pair of collections
  */

libraries/stdlib/src/generated/_Iterators.kt

@@ -225,6 +225,25 @@ public fun <T: Comparable<T>> Iterator<T>.max() : T? {
     return max
 }
 
+/**
+ * Returns the first element yielding the largest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>, T: Any> Iterator<T>.maxBy(f: (T) -> R) : T? {
+    if (!hasNext()) return null
+    
+    var maxElem = next()
+    var maxValue = f(maxElem)
+    while (hasNext()) {
+        val e = next()
+        val v = f(e)
+        if (maxValue < v) {
+           maxElem = e
+           maxValue = v
+        }
+    }
+    return maxElem
+}
+
 /**
  * Returns the smallest element or null if there are no elements
  */
@@ -238,6 +257,25 @@ public fun <T: Comparable<T>> Iterator<T>.min() : T? {
     return min
 }
 
+/**
+ * Returns the first element yielding the smallest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>, T: Any> Iterator<T>.minBy(f: (T) -> R) : T? {
+    if (!hasNext()) return null
+    
+    var minElem = next()
+    var minValue = f(minElem)
+    while (hasNext()) {
+        val e = next()
+        val v = f(e)
+        if (minValue > v) {
+           minElem = e
+           minValue = v
+        }
+    }
+    return minElem
+}
+
 /**
  * Partitions this collection into a pair of collections
  */

libraries/stdlib/src/generated/_LongArrays.kt

@@ -238,6 +238,25 @@ public fun LongArray.max() : Long? {
     return max
 }
 
+/**
+ * Returns the first element yielding the largest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> LongArray.maxBy(f: (Long) -> R) : Long? {
+    if (isEmpty()) return null
+    
+    var maxElem = this[0]
+    var maxValue = f(maxElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (maxValue < v) {
+           maxElem = e
+           maxValue = v
+        }
+    }
+    return maxElem
+}
+
 /**
  * Returns the smallest element or null if there are no elements
  */
@@ -251,6 +270,25 @@ public fun LongArray.min() : Long? {
     return min
 }
 
+/**
+ * Returns the first element yielding the smallest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> LongArray.minBy(f: (Long) -> R) : Long? {
+    if (size == 0) return null
+    
+    var minElem = this[0]
+    var minValue = f(minElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (minValue > v) {
+           minElem = e
+           minValue = v
+        }
+    }
+    return minElem
+}
+
 /**
  * Partitions this collection into a pair of collections
  */

libraries/stdlib/src/generated/_ShortArrays.kt

@@ -238,6 +238,25 @@ public fun ShortArray.max() : Short? {
     return max
 }
 
+/**
+ * Returns the first element yielding the largest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> ShortArray.maxBy(f: (Short) -> R) : Short? {
+    if (isEmpty()) return null
+    
+    var maxElem = this[0]
+    var maxValue = f(maxElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (maxValue < v) {
+           maxElem = e
+           maxValue = v
+        }
+    }
+    return maxElem
+}
+
 /**
  * Returns the smallest element or null if there are no elements
  */
@@ -251,6 +270,25 @@ public fun ShortArray.min() : Short? {
     return min
 }
 
+/**
+ * Returns the first element yielding the smallest value of the given function or null if there are no elements
+ */
+public inline fun <R: Comparable<R>> ShortArray.minBy(f: (Short) -> R) : Short? {
+    if (size == 0) return null
+    
+    var minElem = this[0]
+    var minValue = f(minElem)
+    for (i in 1..lastIndex) {
+        val e = this[i]
+        val v = f(e)
+        if (minValue > v) {
+           minElem = e
+           minValue = v
+        }
+    }
+    return minElem
+}
+
 /**
  * Partitions this collection into a pair of collections
  */

libraries/stdlib/test/ArraysJVMTest.kt

@@ -105,6 +105,38 @@ class ArraysJVMTest {
         expect(3.0, { doubleArray(2.0, 3.0).max() })
     }
 
+    test fun minBy() {
+        expect(null, { intArray().minBy { it } })
+        expect(1, { intArray(1).minBy { it } })
+        expect(3, { intArray(2, 3).minBy { -it } })
+        expect(2000000000000, { longArray(3000000000000, 2000000000000).minBy { it + 1 } })
+        expect(1, { byteArray(1, 3, 2).minBy { it * it } })
+        expect(3, { shortArray(3, 2).minBy { "a" } })
+        expect(2.0, { floatArray(3.0, 2.0).minBy { it.toString() } })
+        expect(2.0, { doubleArray(2.0, 3.0).minBy { Math.sqrt(it) } })
+    }
+
+    test fun minIndex() {
+        val a = intArray(1, 7, 9, -42, 54, 93)
+        expect(3, { a.indices.minBy { a[it] } })
+    }
+
+    test fun maxBy() {
+        expect(null, { intArray().maxBy { it } })
+        expect(1, { intArray(1).maxBy { it } })
+        expect(2, { intArray(2, 3).maxBy { -it } })
+        expect(3000000000000, { longArray(3000000000000, 2000000000000).maxBy { it + 1 } })
+        expect(3, { byteArray(1, 3, 2).maxBy { it * it } })
+        expect(3, { shortArray(3, 2).maxBy { "a" } })
+        expect(3.0, { floatArray(3.0, 2.0).maxBy { it.toString() } })
+        expect(3.0, { doubleArray(2.0, 3.0).maxBy { Math.sqrt(it) } })
+    }
+
+    test fun maxIndex() {
+        val a = intArray(1, 7, 9, 239, 54, 93)
+        expect(3, { a.indices.maxBy { a[it] } })
+    }
+
     test fun sum() {
         expect(0) { intArray().sum() }
         expect(14) { intArray(2, 3, 9).sum() }

libraries/stdlib/test/ArraysTest.kt

@@ -119,6 +119,34 @@ class ArraysTest {
         expect("b", { array("a", "b").max() })
     }
 
+    test fun minBy() {
+        expect(null, { array<Int>().minBy { it } })
+        expect(1, { array(1).minBy { it } })
+        expect(3, { array(2, 3).minBy { -it } })
+        expect('a', { array('a', 'b').minBy { "x$it" } })
+        expect("b", { array("b", "abc").minBy { it.length } })
+    }
+
+    test fun maxBy() {
+        expect(null, { array<Int>().maxBy { it } })
+        expect(1, { array(1).maxBy { it } })
+        expect(2, { array(2, 3).maxBy { -it } })
+        expect('b', { array('a', 'b').maxBy { "x$it" } })
+        expect("abc", { array("b", "abc").maxBy { it.length } })
+    }
+
+    test fun minByEvaluateOnce() {
+        var c = 0
+        expect(1, { array(5, 4, 3, 2, 1).minBy { c++; it * it } })
+        assertEquals(5, c)
+    }
+
+    test fun maxByEvaluateOnce() {
+        var c = 0
+        expect(5, { array(5, 4, 3, 2, 1).maxBy { c++; it * it } })
+        assertEquals(5, c)
+    }
+
     test fun sum() {
         expect(0) { array<Int>().sum() }
         expect(14) { array(2, 3, 9).sum() }

libraries/stdlib/test/CollectionTest.kt

@@ -436,6 +436,44 @@ class CollectionTest {
         expect(3, { listOf(2, 3).iterator().max() })
     }
 
+    test fun minBy() {
+        expect(null, { listOf<Int>().minBy { it } })
+        expect(1, { listOf(1).minBy { it } })
+        expect(3, { listOf(2, 3).minBy { -it } })
+        expect('a', { listOf('a', 'b').minBy { "x$it" } })
+        expect("b", { listOf("b", "abc").minBy { it.length } })
+        expect(null, { listOf<Int>().iterator().minBy { it } })
+        expect(3, { listOf(2, 3).iterator().minBy { -it } })
+    }
+
+    test fun maxBy() {
+        expect(null, { listOf<Int>().maxBy { it } })
+        expect(1, { listOf(1).maxBy { it } })
+        expect(2, { listOf(2, 3).maxBy { -it } })
+        expect('b', { listOf('a', 'b').maxBy { "x$it" } })
+        expect("abc", { listOf("b", "abc").maxBy { it.length } })
+        expect(null, { listOf<Int>().iterator().maxBy { it } })
+        expect(2, { listOf(2, 3).iterator().maxBy { -it } })
+    }
+
+    test fun minByEvaluateOnce() {
+        var c = 0
+        expect(1, { listOf(5, 4, 3, 2, 1).minBy { c++; it * it } })
+        assertEquals(5, c)
+        c = 0
+        expect(1, { listOf(5, 4, 3, 2, 1).iterator().minBy { c++; it * it } })
+        assertEquals(5, c)
+    }
+
+    test fun maxByEvaluateOnce() {
+        var c = 0
+        expect(5, { listOf(5, 4, 3, 2, 1).maxBy { c++; it * it } })
+        assertEquals(5, c)
+        c = 0
+        expect(5, { listOf(5, 4, 3, 2, 1).iterator().maxBy { c++; it * it } })
+        assertEquals(5, c)
+    }
+
     test fun sum() {
         expect(0) { ArrayList<Int>().sum() }
         expect(14) { arrayListOf(2, 3, 9).sum() }