How to convert/transform a collection to another collection by element's property?
Solution 1
it's easy to do in Kotlin:
// v--- the variable type can be removed
var nameMap: MutableList<String> = persons.map { it.name }.toMutableList();
IF you want an immutable List
, it can simplify as below:
// v--- the variable type can be removed
var nameMap: List<String> = persons.map { it.name };
OR using function reference expression instead:
var nameMap = persons.map(Person::name);
Solution 2
If you want to map model then do this.
var nameMap: List<Model> = persons.map { Model(it.name,it.number) };
Solution 3
Option 1:
inline fun <reified T, Y> MutableList<T>.listOfField(property: KMutableProperty1<T, Y?>): MutableList<Y> {
val yy = ArrayList<Y>()
this.forEach { t: T ->
yy.add(property.get(t) as Y)
}
return yy
}
Usage:
val serviceIds = services.listOfField(ServiceModel::id)
Option 2:
var serviceIds: MutableList<String> = services.map { it.id }.toMutableList()
Option 3:
Function Reference
var serviceIds = services.map(Person::id)
Parker
Duke 2013 Microsoft PM '13-Present I like Python. Also, turtles.
Updated on July 05, 2022Comments
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Parker almost 2 years
If I have a collection of an object in Kotlin, is there a quick way to get a collection of a certain property of those objects? I looked at a list of collection operations for Kotlin, but nothing stood out for me (but I may have overlooked something)
In python it would be akin to:
[person.name for person in persons]
And I'd prefer to use a collections function instead of doing:
var nameMap = mutableListOf<String>() persons.forEach{person -> nameMap.add(person.name)}
I'm pretty lacking in knowledge of filtering/lambda functions and anything other than list comprehension, so apologies if this is a simple question