Is there a method that runs on a collection of objects, returning a collection that contains a specific field from the original collection? ( I tried searching through all collection methods with no success, no google help too) For example:

data class Dog(val id: Int, val name: String)

val dogs = arrayListOf(Dog(0, "jack"), Dog(1,"Jacky"), Dog(2, "Chan"))
val listOfDogsId = dogs.somecoolmethodhere(it.id) // listOfDogsId = arrayListOf<Int>(0,1,2)

it sounds like you’re looking for map: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/map.html

You might want to perform a map over the original collection.Selecting the id

Exactly!! Thank you my friends @Brian @Javier Troconis (for anyone needing this, this code solved my issue):

val listOfDogsId = dogs.map{it.id}

@Ofir Bar The correct syntax is

val listOfDogIds = dogs.map { it.id }

Or

val listOfDogIds = dogs.map(Dog::id)

if you prefer function references

Thanks, I fixed my example @tseisel