jvmMain.kotlin.collections.GroupingJVM.kt Maven / Gradle / Ivy
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Kotlin Standard Library for JVM
/*
* Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
* Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
*/
@file:kotlin.jvm.JvmName("GroupingKt")
@file:kotlin.jvm.JvmMultifileClass
package kotlin.collections
/**
* Groups elements from the [Grouping] source by key and counts elements in each group.
*
* @return a [Map] associating the key of each group with the count of elements in the group.
*
* @sample samples.collections.Grouping.groupingByEachCount
*/
@SinceKotlin("1.1")
public actual fun Grouping.eachCount(): Map =
// fold(0) { acc, e -> acc + 1 } optimized for boxing
foldTo(destination = mutableMapOf(),
initialValueSelector = { _, _ -> kotlin.jvm.internal.Ref.IntRef() },
operation = { _, acc, _ -> acc.apply { element += 1 } })
.mapValuesInPlace { it.value.element }
/*
/**
* Groups elements from the [Grouping] source by key and sums values provided by the [valueSelector] function for elements in each group.
*
* @return a [Map] associating the key of each group with the sum of elements in the group.
*/
@SinceKotlin("1.X")
public inline fun Grouping.eachSumOf(valueSelector: (T) -> Int): Map =
// fold(0) { acc, e -> acc + valueSelector(e)} optimized for boxing
foldTo( destination = mutableMapOf(),
initialValueSelector = { _, _ -> kotlin.jvm.internal.Ref.IntRef() },
operation = { _, acc, e -> acc.apply { element += valueSelector(e) } })
.mapValuesInPlace { it.value.element }
*/
@PublishedApi
@kotlin.internal.InlineOnly
@Suppress("UNCHECKED_CAST") // tricks with erased generics go here, do not repeat on reified platforms
internal inline fun MutableMap.mapValuesInPlace(f: (Map.Entry) -> R): MutableMap {
entries.forEach {
(it as MutableMap.MutableEntry).setValue(f(it))
}
return (this as MutableMap)
}