https://kotlinlang.org logo
Channels
100daysofcode
100daysofkotlin
100daysofkotlin-2021
advent-of-code
aem
ai
alexa
algeria
algolialibraries
amsterdam
android
android-architecture
android-databinding
android-studio
androidgithubprojects
androidthings
androidx
androidx-xprocessing
anime
anko
announcements
apollo-kotlin
appintro
arabic
argentina
arkenv
arksemdevteam
armenia
arrow
arrow-contributors
arrow-meta
ass
atlanta
atm17
atrium
austin
australia
austria
awesome-kotlin
ballast
bangladesh
barcelona
bayarea
bazel
beepiz-libraries
belgium
benchmarks
berlin
big-data
books
boston
brazil
brikk
budapest
build
build-tools
bulgaria
bydgoszcz
cambodia
canada
carrat
carrat-dev
carrat-feed
chicago
chile
china
chucker
cincinnati-user-group
cli
clikt
cloudfoundry
cn
cobalt
code-coverage
codeforces
codemash-precompiler
codereview
codingame
codingconventions
coimbatore
collaborations
colombia
colorado
communities
competitive-programming
competitivecoding
compiler
compose
compose-android
compose-desktop
compose-hiring
compose-ios
compose-mp
compose-ui-showcase
compose-wear
compose-web
confetti
connect-audit-events
corda
cork
coroutines
couchbase
coursera
croatia
cryptography
cscenter-course-2016
cucumber-bdd
cyprus
czech
dagger
data2viz
databinding
datascience
dckotlin
debugging
decompose
decouple
denmark
deprecated
detekt
detekt-hint
dev-core
dfw
docs-revamped
dokka
domain-driven-design
doodle
dsl
dublin
dutch
eap
eclipse
ecuador
edinburgh
education
effective-kotlin
effectivekotlin
emacs
embedded-kotlin
estatik
event21-community-content
events
exposed
failgood
fb-internal-demo
feed
firebase
flow
fluid-libraries
forkhandles
forum
fosdem
fp-in-kotlin
framework-elide
freenode
french
fritz2
fuchsia
functional
funktionale
gamedev
ge-kotlin
general-advice
georgia
geospatial
german-lang
getting-started
github-workflows-kt
glance
godot-kotlin
google-io
gradle
graphic
graphkool
graphql
graphql-kotlin
graviton-browser
greece
grpc
gsoc
gui
hackathons
hacktoberfest
hamburg
hamkrest
helios
helsinki
hexagon
hibernate
hikari-cp
hire-me
hiring
hiring-french
hongkong
hoplite
http4k
hungary
hyderabad
image-processing
india
indonesia
inkremental
intellij
intellij-plugins
intellij-tricks
internships
introduce-yourself
io
ios
iran
israel
istanbulcoders
italian
jackson-kotlin
jadx
japanese
jasync-sql
java-to-kotlin-refactoring
javadevelopers
javafx
javalin
javascript
jdbi
jhipster-kotlin
jobsworldwide
jpa
jshdq
juul-libraries
jvm-ir-backend-feedback
jxadapter
k2-early-adopters
kaal
kafka
kakao
kalasim
kapt
karachi
karg
karlsruhe
kash_shell
kaskade
kbuild
kdbc
kgen-doc-tools
kgraphql
kinta
klaxon
klock
kloudformation
kmdc
kmm-español
kmongo
knbt
knote
koalaql
koans
kobalt
kobweb
kodein
kodex
kohesive
koin
koin-dev
komapper
kondor-json
kong
kontent
kontributors
korau
korean
korge
korim
korio
korlibs
korte
kotest
kotest-contributors
kotless
kotlick
kotlin-asia
kotlin-beam
kotlin-by-example
kotlin-csv
kotlin-data-storage
kotlin-foundation
kotlin-fuel
kotlin-in-action
kotlin-inject
kotlin-latam
kotlin-logging
kotlin-multiplatform-contest
kotlin-mumbai
kotlin-native
kotlin-pakistan
kotlin-plugin
kotlin-pune
kotlin-roadmap
kotlin-samples
kotlin-sap
kotlin-serbia
kotlin-spark
kotlin-szeged
kotlin-website
kotlinacademy
kotlinbot
kotlinconf
kotlindl
kotlinforbeginners
kotlingforbeginners
kotlinlondon
kotlinmad
kotlinprogrammers
kotlinsu
kotlintest
kotlintest-devs
kotlintlv
kotlinultimatechallenge
kotlinx-datetime
kotlinx-files
kotlinx-html
kotrix
kotson
kovenant
kprompt
kraph
krawler
kroto-plus
ksp
ktcc
ktfmt
ktlint
ktor
ktp
kubed
kug-leads
kug-torino
kvision
kweb
lambdaworld_cadiz
lanark
language-evolution
language-proposals
latvia
leakcanary
leedskotlinusergroup
lets-have-fun
libgdx
libkgd
library-development
lincheck
linkeddata
lithuania
london
losangeles
lottie
love
lychee
macedonia
machinelearningbawas
madrid
malaysia
mathematics
meetkotlin
memes
meta
metro-detroit
mexico
miami
micronaut
minnesota
minutest
mirror
mockk
moko
moldova
monsterpuzzle
montreal
moonbean
morocco
motionlayout
mpapt
mu
multiplatform
mumbai
munich
mvikotlin
mvrx
myndocs-oauth2-server
naming
navigation-architecture-component
nepal
new-mexico
new-zealand
newname
nigeria
nodejs
norway
npm-publish
nyc
oceania
ohio-kotlin-users
oldenburg
oolong
opensource
orbit-mvi
osgi
otpisani
package-search
pakistan
panamá
pattern-matching
pbandk
pdx
peru
philippines
phoenix
pinoy
pocketgitclient
polish
popkorn
portugal
practical-functional-programming
proguard
prozis-android-backup
pyhsikal
python
python-contributors
quasar
random
re
react
reaktive
realm
realworldkotlin
reductor
reduks
redux
redux-kotlin
refactoring-to-kotlin
reflect
refreshversions
reports
result
rethink
revolver
rhein-main
rocksdb
romania
room
rpi-pico
rsocket
russian
russian_feed
russian-kotlinasfirst
rx
rxjava
san-diego
science
scotland
scrcast
scrimage
script
scripting
seattle
serialization
server
sg-user-group
singapore
skia-wasm-interop-temp
skrape-it
slovak
snake
sofl-user-group
southafrica
spacemacs
spain
spanish
speaking
spek
spin
splitties
spotify-mobius
spring
spring-security
squarelibraries
stackoverflow
stacks
stayhungrystayfoolish
stdlib
stlouis
strife-discord-lib
strikt
students
stuttgart
sudan
swagger-gradle-codegen
swarm
sweden
swing
swiss-user-group
switzerland
talking-kotlin
tallinn
tampa
teamcity
tegal
tempe
tensorflow
terminal
test
testing
testtestest
texas
tgbotapi
thailand
tornadofx
touchlab-tools
training
tricity-kotlin-user-group
trójmiasto
truth
tunisia
turkey
turkiye
twitter-feed
uae
udacityindia
uk
ukrainian
uniflow
unkonf
uruguay
utah
uuid
vancouver
vankotlin
vertx
videos
vienna
vietnam
vim
vkug
vuejs
web-mpp
webassembly
webrtc
wimix_sentry
wwdc
zircon
Powered by
Title
d

Daniele B

10/16/2020, 1:06 AM
mylist.zip(mylist.drop(1)) { a, b -> myfunction(a,b) }
is there a way to zip 3 lists instead of 2? something equivalent to this?
zip(mylist, mylist.drop(1), mylist.drop(2)) { a, b, c -> myfunction(a,b,c) }
I would like to create a new list of values, which are calculated based on the latest 3 values
r

Ruckus

10/16/2020, 1:49 AM
I think you want the
windowed
function
d

Daniele B

10/16/2020, 1:57 AM
ok, I get the meaning of windowed now:
mylist.windowed(2).map {
    myfunction(it.get(0),it.get(1),it.get(2))
}
correct?
e

ephemient

10/16/2020, 2:04 AM
yes, though feel free to use the operator
mylist.windowed(2).map {
    myFunction(it[0], it[1], it[2])
}
r

Ruckus

10/16/2020, 2:06 AM
Or destructure
mylist.windowed(2).map { (a, b, c) ->
    myFunction(a, b, c)
}
d

Daniele B

10/16/2020, 2:08 AM
@ephemient thanks! @Ruckus actually in my case, I need something like this:
mylist.windowed(8).map {
    myFunction(it[0], it[1], it[7])
}
because I need to calculate differences by the day and by the week, so I need to take the value 1 index later and 7 indexes later
on the documentation is written that
windowed()
is returning a list for each window: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/windowed.html I wonder if that ends up being too expensive, and whether it’s more efficient to just use an imperative loop
r

Ruckus

10/16/2020, 2:18 AM
An imperative loop would be more efficient, but whether it matters is a matter of testing.
☝️ 1
e

ephemient

10/16/2020, 2:20 AM
if
mylist
has random access then
List(mylist.size - 8) { myFunction(mylist[it], mylist[it + 1], mylist[it + 7]) }
would inline to the same as an imperative loop
❤️ 1
d

Daniele B

10/16/2020, 2:21 AM
what is
random access
actually?
e

ephemient

10/16/2020, 2:22 AM
array, arraylist, not linkedlist
r

Ruckus

10/16/2020, 2:23 AM
A list when
list[n]
is constant time, not linear
d

Daniele B

10/16/2020, 2:25 AM
I watched the Kotlin online event this week, and I heard Roman Elizarov saying to always prefer Lists to Arrays
I don’t even understand the difference to be honest
e

ephemient

10/16/2020, 2:26 AM
the distinction comes from java (there is no difference in representation on kotlin/js)
d

Daniele B

10/16/2020, 2:27 AM
I guess Roman was referring to the Kotlin/JVM
but I am doing multiplatform, so it would make a difference for me
e

ephemient

10/16/2020, 2:28 AM
Array comes from a time before generics, and as such has some unique and special treatment by the JVM, like built-in primitive types
List actually fits into the iterable/collection type hierarchy and works like everything else you'd expect
the default implementation is ArrayList which does use Array internally, but as a user all you care about is that it is amortized O(1) access
d

Daniele B

10/16/2020, 2:34 AM
so this would not work if I created my list with
listOf
?
List(mylist.size - 8) { myFunction(mylist[it], mylist[it + 1], mylist[it + 7]) }
e

ephemient

10/16/2020, 2:35 AM
it will work.
listOf()
is backed by an
ArrayList
(implementation detail, but even if it changes in the future it will still work)
d

Daniele B

10/16/2020, 2:36 AM
so would you say the above is more efficient than?
mylist.windowed(8).map {
    myFunction(it[0], it[1], it[7])
}
e

ephemient

10/16/2020, 2:36 AM
yes, it doesn't need to be indirected through the window list view
👍 1
but it's almost certainly a smaller difference that you should care about
... and I realized it's slightly wrong; it should be
List(mylist.size - 7)
to get the last window. that's what happens easily when working without the abstractions
👍 1
v

Vampire

10/16/2020, 7:14 AM
Don't try to micro-optimize up front. 80% of the time your program is running is spent in 20% of the code (rough thumb rule). There is no real point in optimizing the other 80%. 1. Make your code working correctly 2. Make your code pretty (refactoring) 3. Optimize your code, but only where you actually have a performance problem according to testing or profiling
👍 2