Merge pull request #9905 from anirban99/feature/ktln-154/collection-aggregate-operations-in-kotlin

KTLN-154 : Collection Aggregate Operations in Kotlin

core-kotlin-modules/core-kotlin-collections-2/README.md

@@ -0,0 +1,7 @@
+## Core Kotlin Collections
+
+This module contains articles about core Kotlin collections.
+
+### Relevant articles:
+
+

core-kotlin-modules/core-kotlin-collections-2/pom.xml

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-kotlin-collections-2</artifactId>
+    <name>core-kotlin-collections-2</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-kotlin-modules</groupId>
+        <artifactId>core-kotlin-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.jetbrains.kotlin</groupId>
+            <artifactId>kotlin-stdlib-jdk8</artifactId>
+            <version>${kotlin.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-math3</artifactId>
+            <version>${commons-math3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.jetbrains.kotlin</groupId>
+            <artifactId>kotlin-test</artifactId>
+            <version>${kotlin.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <kotlin.version>1.3.30</kotlin.version>
+        <commons-math3.version>3.6.1</commons-math3.version>
+        <assertj.version>3.10.0</assertj.version>
+    </properties>
+
+</project>

core-kotlin-modules/core-kotlin-collections-2/src/main/kotlin/com/baeldung/aggregate/AggregateOperations.kt

@@ -0,0 +1,107 @@
+package com.baeldung.aggregate
+
+class AggregateOperations {
+    private val numbers = listOf(1, 15, 3, 8)
+
+    fun countList(): Int {
+        return numbers.count()
+    }
+
+    fun sumList(): Int {
+        return numbers.sum()
+    }
+
+    fun averageList(): Double {
+        return numbers.average()
+    }
+
+    fun maximumInList(): Int? {
+        return numbers.max()
+    }
+
+    fun minimumInList(): Int? {
+        return numbers.min()
+    }
+
+    fun maximumByList(): Int? {
+        return numbers.maxBy { it % 5 }
+    }
+
+    fun minimumByList(): Int? {
+        return numbers.minBy { it % 5 }
+    }
+
+    fun maximumWithList(): String? {
+        val strings = listOf("Berlin", "Kolkata", "Prague", "Barcelona")
+        return strings.maxWith(compareBy { it.length % 4 })
+    }
+
+    fun minimumWithList(): String? {
+        val strings = listOf("Berlin", "Kolkata", "Prague", "Barcelona")
+        return strings.minWith(compareBy { it.length % 4 })
+    }
+
+    fun sumByList(): Int {
+        return numbers.sumBy { it * 5 }
+    }
+
+    fun sumByDoubleList(): Double {
+        return numbers.sumByDouble { it.toDouble() / 8 }
+    }
+
+    fun foldList(): Int {
+        return numbers.fold(100) { total, it ->
+            println("total = $total, it = $it")
+            total - it
+        } // ((((100 - 1)-15)-3)-8) = 73
+    }
+
+    fun foldRightList(): Int {
+        return numbers.foldRight(100) { it, total ->
+            println("total = $total, it = $it")
+            total - it
+        }  // ((((100-8)-3)-15)-1) = 73
+    }
+
+    fun foldIndexedList(): Int {
+        return numbers.foldIndexed(100) { index, total, it ->
+            println("total = $total, it = $it, index = $index")
+            if (index.minus(2) >= 0) total - it else total
+        } // ((100 - 3)-8) = 89
+    }
+
+    fun foldRightIndexedList(): Int {
+        return numbers.foldRightIndexed(100) { index, it, total ->
+            println("total = $total, it = $it, index = $index")
+            if (index.minus(2) >= 0) total - it else total
+        } // ((100 - 8)-3) = 89
+    }
+
+    fun reduceList(): Int {
+        return numbers.reduce { total, it ->
+            println("total = $total, it = $it")
+            total - it
+        } // (((1 - 15)-3)-8) = -25
+    }
+
+    fun reduceRightList(): Int {
+        return numbers.reduceRight() { it, total ->
+            println("total = $total, it = $it")
+            total - it
+        } // ((8-3)-15)-1) = -11
+    }
+
+    fun reduceIndexedList(): Int {
+        return numbers.reduceIndexed { index, total, it ->
+            println("total = $total, it = $it, index = $index")
+            if (index.minus(2) >= 0) total - it else total
+        } // ((1-3)-8) = -10
+    }
+
+    fun reduceRightIndexedList(): Int {
+        return numbers.reduceRightIndexed { index, it, total ->
+            println("total = $total, it = $it, index = $index")
+            if (index.minus(2) >= 0) total - it else total
+        } // ((8-3) = 5
+    }
+}

core-kotlin-modules/core-kotlin-collections-2/src/test/kotlin/com/baeldung/aggregate/AggregateOperationsUnitTest.kt

@@ -0,0 +1,104 @@
+package com.baeldung.aggregate
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+class AggregateOperationsUnitTest {
+
+    private val classUnderTest: AggregateOperations = AggregateOperations()
+
+    @Test
+    fun whenCountOfList_thenReturnsValue() {
+        assertEquals(4, classUnderTest.countList())
+    }
+
+    @Test
+    fun whenSumOfList_thenReturnsTotalValue() {
+        assertEquals(27, classUnderTest.sumList())
+    }
+
+    @Test
+    fun whenAverageOfList_thenReturnsValue() {
+        assertEquals(6.75, classUnderTest.averageList())
+    }
+
+    @Test
+    fun whenMaximumOfList_thenReturnsMaximumValue() {
+        assertEquals(15, classUnderTest.maximumInList())
+    }
+
+    @Test
+    fun whenMinimumOfList_thenReturnsMinimumValue() {
+        assertEquals(1, classUnderTest.minimumInList())
+    }
+
+    @Test
+    fun whenMaxByList_thenReturnsLargestValue() {
+        assertEquals(3, classUnderTest.maximumByList())
+    }
+
+    @Test
+    fun whenMinByList_thenReturnsSmallestValue() {
+        assertEquals(15, classUnderTest.minimumByList())
+    }
+
+    @Test
+    fun whenMaxWithList_thenReturnsLargestValue(){
+        assertEquals("Kolkata", classUnderTest.maximumWithList())
+    }
+
+    @Test
+    fun whenMinWithList_thenReturnsSmallestValue(){
+        assertEquals("Barcelona", classUnderTest.minimumWithList())
+    }
+
+    @Test
+    fun whenSumByList_thenReturnsIntegerValue(){
+        assertEquals(135, classUnderTest.sumByList())
+    }
+
+    @Test
+    fun whenSumByDoubleList_thenReturnsDoubleValue(){
+        assertEquals(3.375, classUnderTest.sumByDoubleList())
+    }
+
+    @Test
+    fun whenFoldList_thenReturnsValue(){
+        assertEquals(73, classUnderTest.foldList())
+    }
+
+    @Test
+    fun whenFoldRightList_thenReturnsValue(){
+        assertEquals(73, classUnderTest.foldRightList())
+    }
+
+    @Test
+    fun whenFoldIndexedList_thenReturnsValue(){
+        assertEquals(89, classUnderTest.foldIndexedList())
+    }
+
+    @Test
+    fun whenFoldRightIndexedList_thenReturnsValue(){
+        assertEquals(89, classUnderTest.foldRightIndexedList())
+    }
+
+    @Test
+    fun whenReduceList_thenReturnsValue(){
+        assertEquals(-25, classUnderTest.reduceList())
+    }
+
+    @Test
+    fun whenReduceRightList_thenReturnsValue(){
+        assertEquals(-11, classUnderTest.reduceRightList())
+    }
+
+    @Test
+    fun whenReduceIndexedList_thenReturnsValue(){
+        assertEquals(-10, classUnderTest.reduceIndexedList())
+    }
+
+    @Test
+    fun whenReduceRightIndexedList_thenReturnsValue(){
+        assertEquals(5, classUnderTest.reduceRightIndexedList())
+    }
+}

core-kotlin-modules/pom.xml

@@ -21,6 +21,7 @@
         <module>core-kotlin-advanced</module>
         <module>core-kotlin-annotations</module>
         <module>core-kotlin-collections</module>
+        <module>core-kotlin-collections-2</module>
         <module>core-kotlin-concurrency</module>
         <module>core-kotlin-date-time</module>
         <module>core-kotlin-design-patterns</module>