Hello! What's the best way to get next item in Set? For example, I have Set{2,8,3,4}. And If I take item "8", how can I get an item with number "3" from the list ? I can't just find item 3, I need find solution to take next item in Set. The main goal to add previous and next button on Details screen to be able going through the set.

You can use iterator for this

Sets dont have a defined ordering. Unless they are NavigableSet, I.e. TreeSet, it will be arbitrary.

Default set implementation used in kotlin for generic set builder is sorted, but I agree, Set probably not the best data structure for this

Ok, thanks, I'll try to use NavigableSet

Whichever

Iterable<Int>

you use:

val next: Int? = iterable.dropWhile { it != 8 }.getOrNull(1)

So would apply to all

Set

implementations, or

List

implementations.

Not the most efficient implementation tho, it creates intermediate list

I took into account the use case.

The main goal to add previous and next button on Details screen to be able going through the set.

Yes, I understand, but it can be achieved without intermediate collection creation (many ways actually)

Still, how do you suggest using the

NavigableSet

? And why not a

SortedSet

?

SortedSet is an interface NavigatableSet is an implementation of this interface

That's trivial. The point was that set makes no sense.

Yes, you right, sorry

If you wanted to avoid intermediate list creation:

val next: Int? = iterable
        .asSequence()
        .dropWhile { it != 8 }
        .elementAtOrNull(1)

TreeSet is implementation

I'm just not sure what you're suggesting, trivial or not. Are you suggesting a Java style

while

loop?

But it still doesn't make sense because elements will be displayed in arbitrary order. Unless that's what he wants, I'm recommending to use something that does have a defined ordering. The ordering of your idea is only defined if the set is sorted.

What's the best sorted set in my case?

I just said

iterable

So it works for the

TreeSet

or a

List

.

Well, we've gone off and assumed that you have integers in your set. Is that right?

I would use a

List

.

YEs

Yeah if you can use a list, use a list.

I can't use List, because I need to accumulate only unique data

Even if you have a set then:

val list: List<Int> = set.sortedBy { it } 
    
    val next: Int? = list
        .asSequence()
        .dropWhile { it != 8 }
        .elementAtOrNull(1)

You can remove duplicates from list using extension function distinct()

Thanks guys, I chose TreeSet. And now I can take lower and higher item. It's really convenient. But now I'm stuck with implementing Comparable. Because I use in Set some Objects (Int was for understanding a problem). What's the best way to implement compareTo method? In my object I have field "String" (hex data).

Called it!

it is far easier to specify that sort order than support

Comparable

, or write a

Comparator

which is what you need to do if you use

TreeSet

.

I tried to do it in your error, but I had an error

say what?

you need to specify the sort order, e.g.

sortedBy { it.someField }

ok, you are right

but still, maybe go with the treeset, the comparators don't look too bad in Kotlin

Yes, TreeSet was good idea, I just had a problem with a comporator. I'll try you implementation for compareTo. Thanks

You can also give the same comparators to sort

set.sortedWith(byField1.then(byField2Descending))

I implemented Comparable in my object. TreeSet works fine with this implementation: override fun compareTo(other: BeaconData): Int { return this.data.compareTo(other.data) } Thanks )