CODEWITHSUNDEEP
kotlinfunctional-programming
Matt
Matt

Reputation: 1308

Map value to every value from set

Let's say I have classes:

class SomeClass(
        val name: String
)

data class MyClass (
        val setValues: Set<SomeClass>,
        val intValue: Int
)

Then I create set like this:

val someClass1 = SomeClass("a")
val someClass2 = SomeClass("b")
val someClass3 = SomeClass("c")
val someClass4 = SomeClass("d")
val someClass5 = SomeClass("e")
val someClass6 = SomeClass("f")

val val1 = MyClass(setOf(someClass1, someClass2, someClass3), 1)
val val2 = MyClass(setOf(someClass1, someClass4, someClass5), 2)
val val3 = MyClass(setOf(someClass4, someClass5, someClass6), 3)

val setOfMyClass = setOf(val1, val2, val3)

and I want to do some operations on this set setOfMyClass like

val result = set. ...

and as a result get mapping like this:

someClass1 to 1
someClass2 to 1
someClass3 to 1
someClass1 to 2
someClass4 to 2
someClass5 to 2
someClass4 to 3
someClass5 to 3
someClass6 to 3

it probably should be some kind of list.

Upvotes: 1

Views: 76

Answers (3)

Luzian
Luzian

Reputation: 1026

You have a Set<MyClass>, which each contains a Set<SomeClass>. To map a collection of collections into a single collection, usually flatMap is the solution. In your example, combining flatMap on the outer set and map on the inner set gives you a list of mapped pairs.

This gives you a List<Pair<SomeClass, Int>> - which is probably what you want?

val result = setOfMyClass.flatMap { myObject ->
    myObject.setValues.map { it to myObject.intValue }
}

Or if you want it as a Map<SomeClass, Int>, simply do the same as above and:

result.toMap()

Upvotes: 2

Moritz Gro&#223;
Moritz Gro&#223;

Reputation: 1490

I'm not sure if I understand your question, but I'll give it a try.

Let's say SomeClass was Int and you want to compute intValue + x for every element x from setValues.

Int this case you'd do myClassObject.setValues.map{Pair(it, myClassObject.intValue)} and receive a list of the results. The result is a list and not a set, because some results could appear multiple times (as the mapping does not need to be injective), and the multiplicity of elements is lost in a set.

Upvotes: 0

syncended
syncended

Reputation: 91

If i'm understand your question, the solution will be: setValues.associateWith { intValue } that will return Map<SomeClass, Int>

Upvotes: 0

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