Merge pull request #9905 from anirban99/feature/ktln-154/collection-aggregate-operations-in-kotlin
KTLN-154 : Collection Aggregate Operations in Kotlin
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rpvilao
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## Core Kotlin Collections
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This module contains articles about core Kotlin collections.
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### Relevant articles:
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<artifactId>core-kotlin-collections-2</artifactId>
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<name>core-kotlin-collections-2</name>
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<packaging>jar</packaging>
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<parent>
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<groupId>com.baeldung.core-kotlin-modules</groupId>
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<artifactId>core-kotlin-modules</artifactId>
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<version>1.0.0-SNAPSHOT</version>
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</parent>
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<dependencies>
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<dependency>
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<groupId>org.jetbrains.kotlin</groupId>
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<artifactId>kotlin-stdlib-jdk8</artifactId>
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<version>${kotlin.version}</version>
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</dependency>
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-math3</artifactId>
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<version>${commons-math3.version}</version>
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</dependency>
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<dependency>
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<groupId>org.assertj</groupId>
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<artifactId>assertj-core</artifactId>
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<version>${assertj.version}</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.jetbrains.kotlin</groupId>
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<artifactId>kotlin-test</artifactId>
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<version>${kotlin.version}</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<properties>
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<kotlin.version>1.3.30</kotlin.version>
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<commons-math3.version>3.6.1</commons-math3.version>
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<assertj.version>3.10.0</assertj.version>
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</properties>
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</project>
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package com.baeldung.aggregate
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class AggregateOperations {
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private val numbers = listOf(1, 15, 3, 8)
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fun countList(): Int {
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return numbers.count()
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}
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fun sumList(): Int {
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return numbers.sum()
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}
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fun averageList(): Double {
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return numbers.average()
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}
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fun maximumInList(): Int? {
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return numbers.max()
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}
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fun minimumInList(): Int? {
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return numbers.min()
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}
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fun maximumByList(): Int? {
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return numbers.maxBy { it % 5 }
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}
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fun minimumByList(): Int? {
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return numbers.minBy { it % 5 }
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}
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fun maximumWithList(): String? {
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val strings = listOf("Berlin", "Kolkata", "Prague", "Barcelona")
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return strings.maxWith(compareBy { it.length % 4 })
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}
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fun minimumWithList(): String? {
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val strings = listOf("Berlin", "Kolkata", "Prague", "Barcelona")
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return strings.minWith(compareBy { it.length % 4 })
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}
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fun sumByList(): Int {
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return numbers.sumBy { it * 5 }
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}
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fun sumByDoubleList(): Double {
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return numbers.sumByDouble { it.toDouble() / 8 }
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}
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fun foldList(): Int {
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return numbers.fold(100) { total, it ->
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println("total = $total, it = $it")
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total - it
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} // ((((100 - 1)-15)-3)-8) = 73
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}
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fun foldRightList(): Int {
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return numbers.foldRight(100) { it, total ->
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println("total = $total, it = $it")
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total - it
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} // ((((100-8)-3)-15)-1) = 73
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}
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fun foldIndexedList(): Int {
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return numbers.foldIndexed(100) { index, total, it ->
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println("total = $total, it = $it, index = $index")
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if (index.minus(2) >= 0) total - it else total
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} // ((100 - 3)-8) = 89
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}
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fun foldRightIndexedList(): Int {
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return numbers.foldRightIndexed(100) { index, it, total ->
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println("total = $total, it = $it, index = $index")
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if (index.minus(2) >= 0) total - it else total
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} // ((100 - 8)-3) = 89
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}
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fun reduceList(): Int {
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return numbers.reduce { total, it ->
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println("total = $total, it = $it")
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total - it
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} // (((1 - 15)-3)-8) = -25
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}
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fun reduceRightList(): Int {
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return numbers.reduceRight() { it, total ->
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println("total = $total, it = $it")
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total - it
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} // ((8-3)-15)-1) = -11
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}
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fun reduceIndexedList(): Int {
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return numbers.reduceIndexed { index, total, it ->
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println("total = $total, it = $it, index = $index")
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if (index.minus(2) >= 0) total - it else total
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} // ((1-3)-8) = -10
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}
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fun reduceRightIndexedList(): Int {
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return numbers.reduceRightIndexed { index, it, total ->
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println("total = $total, it = $it, index = $index")
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if (index.minus(2) >= 0) total - it else total
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} // ((8-3) = 5
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}
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}
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package com.baeldung.aggregate
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import org.junit.jupiter.api.Test
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import kotlin.test.assertEquals
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class AggregateOperationsUnitTest {
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private val classUnderTest: AggregateOperations = AggregateOperations()
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@Test
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fun whenCountOfList_thenReturnsValue() {
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assertEquals(4, classUnderTest.countList())
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}
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@Test
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fun whenSumOfList_thenReturnsTotalValue() {
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assertEquals(27, classUnderTest.sumList())
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}
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@Test
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fun whenAverageOfList_thenReturnsValue() {
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assertEquals(6.75, classUnderTest.averageList())
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}
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@Test
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fun whenMaximumOfList_thenReturnsMaximumValue() {
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assertEquals(15, classUnderTest.maximumInList())
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}
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@Test
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fun whenMinimumOfList_thenReturnsMinimumValue() {
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assertEquals(1, classUnderTest.minimumInList())
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}
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@Test
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fun whenMaxByList_thenReturnsLargestValue() {
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assertEquals(3, classUnderTest.maximumByList())
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}
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@Test
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fun whenMinByList_thenReturnsSmallestValue() {
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assertEquals(15, classUnderTest.minimumByList())
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}
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@Test
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fun whenMaxWithList_thenReturnsLargestValue(){
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assertEquals("Kolkata", classUnderTest.maximumWithList())
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}
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@Test
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fun whenMinWithList_thenReturnsSmallestValue(){
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assertEquals("Barcelona", classUnderTest.minimumWithList())
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}
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@Test
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fun whenSumByList_thenReturnsIntegerValue(){
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assertEquals(135, classUnderTest.sumByList())
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}
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@Test
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fun whenSumByDoubleList_thenReturnsDoubleValue(){
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assertEquals(3.375, classUnderTest.sumByDoubleList())
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}
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@Test
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fun whenFoldList_thenReturnsValue(){
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assertEquals(73, classUnderTest.foldList())
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}
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@Test
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fun whenFoldRightList_thenReturnsValue(){
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assertEquals(73, classUnderTest.foldRightList())
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}
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@Test
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fun whenFoldIndexedList_thenReturnsValue(){
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assertEquals(89, classUnderTest.foldIndexedList())
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}
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@Test
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fun whenFoldRightIndexedList_thenReturnsValue(){
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assertEquals(89, classUnderTest.foldRightIndexedList())
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}
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@Test
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fun whenReduceList_thenReturnsValue(){
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assertEquals(-25, classUnderTest.reduceList())
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}
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@Test
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fun whenReduceRightList_thenReturnsValue(){
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assertEquals(-11, classUnderTest.reduceRightList())
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}
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@Test
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fun whenReduceIndexedList_thenReturnsValue(){
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assertEquals(-10, classUnderTest.reduceIndexedList())
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}
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@Test
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fun whenReduceRightIndexedList_thenReturnsValue(){
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assertEquals(5, classUnderTest.reduceRightIndexedList())
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}
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}
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@ -21,6 +21,7 @@
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<module>core-kotlin-advanced</module>
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<module>core-kotlin-annotations</module>
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<module>core-kotlin-collections</module>
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<module>core-kotlin-collections-2</module>
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<module>core-kotlin-concurrency</module>
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<module>core-kotlin-date-time</module>
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<module>core-kotlin-design-patterns</module>
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