Question 128192 in Android Studio Question posted in
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Android Studio – How do I filter a list of LiveData objects in Kotlin?

The title might be worded weirdly or unclear, but I am creating a game using android studio and Kotlin as the language. I have a repository that retrieves the score to the game (also stores it):

  val readAllData: LiveData<List<ScoreDB>> = scoreDao.getScore()

Then in my leaderboard composable function I have:

    val scoreList : LiveData<List<ScoreDB>> = vm.readAllData

I want to filter out this list to display the top 10 scores. After scoreList is filtered to only the top ten score, I was going to put it in a lazyColumn using something like this:



                //TODO List highest scores from database in this lazycolumn
                items(10){idx->
                    ScoreRow(idx)


                }

I am stuck on how to filter the scoreList to contain only the top 10 scores and then to display them in the lazy column. Thanks for the help

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2

Answers


  1. 0

    I want to filter out this list to display the top 10 scores.

    OK, so you need

    1. a list
    2. to the sort the list highest to lowest and
    3. to take the first 10 of that:

    So:

    val topTenScores = scoreList  // The live data
    .value // The actual list
    .sortedByDescending { it.score } // The list sorted by ScoreDB.score
    .take(10) // And filtering out the first 10
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  2. 0

    You can use sortedByDescending() to filter the list, and use take() to get the first 10 elements. If you want to show it, you should create a new LivaData to store your filterd list:

    val topTenScoreList : LiveData<List<ScoreDB>> =
Transformations.map(scoreList) {
            it.sortedDescending{ s->s.score }.take(10)
}

    And use topTenScoreList to generate columns

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