Sort a List of objects based in its Sublist method size

Question

I'm trying to make my own "Facebook reaction bar" and I got into a problem, I need to sort a list of objects based in its sublist method size, let me explain!

I have a ReactionModel which has a property "usernames" which is a List of Strings of usernames of those users that used it.

I have a list of ReactionModel which represent the reactions, for example this:

val reactionsList: List<ReactionModel> = listOf(
ReactionModel(listOf("a","b","c")),
ReactionModel(listOf("z")),
ReactionModel(listOf("f","d"))
)

In this case the first one is the largest, after that the third one and finally the second one.

I need to sort the reactionList and got a decreasing of it based on the size of usernames property.

Input:

ReactionModel(listOf("a","b","c")),
ReactionModel(listOf("z")),
ReactionModel(listOf("f","d"))

Output:

ReactionModel(listOf("z")),
ReactionModel(listOf("f","d")),
ReactionModel(listOf("a","b","c"))

I tried using forEach's but without success. I found some question here but is comparing just two list. Hope to find any answer, thanks for your time!!

Edit: Is for Android, so the answer can be in Java or Kotlin

Answer 1

sortedBy can be used for this, I'm assuming the name of the string list in ReactionModel is stringList.

 val sortedList = reactionsList.sortedBy {
                        it.stringList.size
                  }
    

sortedBy doesn't change the existing list, but returns the sorted list.

Answer 2

With Kotlin, you can do it using single line,

reactionsList.sortedByDescending { it.{getYourListHere}.size }