Expressive & Efficient Collection Processing in Kotlin

This Presentation covers Kotlin Collections Examples and Samples of how to do aggregating, transformation, searching, filtering and checks and actions on Kotlin Collections

Presented on September 14th,2019 at Kotlin Everywhere Nairobi Episode 03

1. WELCOME KOTLIN / Everywhere Nairobi Study Jam 3 / 6
2. Expressive & Efficient Collection Processing in Kotlin HARUN WANGEREKA ANDROID DEVELOPER, APPS:LAB
3. Agenda • Basics • Collections Playground • Summary
4. Heavily inspired by Scala
5. Built on top of Java Collections API
6. Defines collections in the kotlin.collections package
7. public interface Iterable<out T> { public operator fun iterator(): Iterator<T> } Basis for all collections
8. Iterator object knows how to iterate over a collection public interface Iterator<out T> { public operator fun next(): T public operator fun hasNext(): Boolean }
9. Next on hierarchy is Collection public interface Collection<out E> : Iterable<E> { public val size: Int public fun isEmpty(): Boolean public operator fun contains(element: @UnsafeVariance E): Boolean override fun iterator(): Iterator<E> public fun containsAll(elements: Collection<@UnsafeVariance E>): Boolean }
10. Next hierarchy is Collection • List • Set • Map
11. Collection Mutable Read-Only • MutableList • MutableSet • MutableMap • List • Set • Map
12. Collections Playground
13. Inspired by the “collector”
14. When the speaker is ready, the collector will appear
16. Summary • Create - We have mutable and read-only • Operators - Functional operations plus,minus, plus assign and minus assign • Transformers - build new collections based on conditions provided • Aggregators - operations that return single value based on collection content • Searching - getting particular elements • Filtering - filter-in with some predicate/condition • Actions - [action] on a particular iterable
17. • Retrieving Collections Parts - Retrieves parts of collections - • Retrieving Single Elements • Collection Ordering • Collections write operations - add(),remove() • List/Set/Map Specific Operations
18. Neat Stuff. The cool way
19. ..the old way var count = 0 var total = 0.0 for (album in albumList){ if (album.genre == "HipHop"){ count ++ total += album.averageRating } } val average = total/ count average.print()
20. The collections.way val avg = albumList.filter { it.genre == "HipHop" } .map { it.averageRating } .average() .print()
21. ..the old way val speakersList :List<SpeakersModel> = getSpeakersInfo() val sessionList : List<SessionsModel> = snapshots.toObjects<SessionsModel>() sessionList.map { sessionModel -> val sessionSpeakerIdList = sessionModel.speaker_id sessionSpeakerIdList.forEach { speakerId -> speakersList.forEach {speakerModel -> if (sessionSpeakerIdList.contains(speakerModel.id)){ sessionModel.speakerList.add(speakerModel) } } } }
22. The collections.way val speakerById : Map<Int, SpeakersModel> = getSpeakerInfo().associateBy { it.id} val sessionList : List<SessionsModel> = snapshots.toObjects() sessionList.onEach { sessionsModel -> sessionsModel.speaker_id.mapNotNull { speakerById[it]?.let { speakerModel -> sessionsModel.speakerList.add(speakerModel) } } }
23. articlesList.filter { it == "Kotlin Collections" }
24. Resources • http://jussi.hallila.com/Kollections/ • https://antonioleiva.com/collection-operations-kotlin/ • https://kotlinlang.org/docs/reference/collections-overview.html • https://github.com/wangerekaharun/CollectionsPlayGround