Comparator for Pair in Kotlin












0














I can write comparator for specialized types in Kotlin
class Comparator() : kotlin.Comparator<Pair<Double, Int>>

But how can I write comparator using generics for all possible types that extend Comparable<...>?






generics kotlin comparator







share|improve this question


















  • 2




    kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/…
    – JB Nizet
    Nov 22 at 19:57
















0














I can write comparator for specialized types in Kotlin
class Comparator() : kotlin.Comparator<Pair<Double, Int>>

But how can I write comparator using generics for all possible types that extend Comparable<...>?






generics kotlin comparator







share|improve this question


















  • 2




    kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/…
    – JB Nizet
    Nov 22 at 19:57














0












0








0







I can write comparator for specialized types in Kotlin
class Comparator() : kotlin.Comparator<Pair<Double, Int>>

But how can I write comparator using generics for all possible types that extend Comparable<...>?






generics kotlin comparator







share|improve this question













I can write comparator for specialized types in Kotlin
class Comparator() : kotlin.Comparator<Pair<Double, Int>>

But how can I write comparator using generics for all possible types that extend Comparable<...>?






generics kotlin comparator




generics kotlin comparator






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Nov 22 at 19:51









Alex Row

337




337








  • 2




    kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/…
    – JB Nizet
    Nov 22 at 19:57














  • 2




    kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/…
    – JB Nizet
    Nov 22 at 19:57








2




2




kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/…
– JB Nizet
Nov 22 at 19:57




kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/…
– JB Nizet
Nov 22 at 19:57












2 Answers
2






active

oldest

votes


















1














You can create comparator, using helping functions - compareBy, compareByDescending, naturalOrder, reverseOrder https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/index.html



For example:



val map = mapOf<Int, String>()

// ... add values to the map

val sortedMap: SortedMap<Int, String> = map.toSortedMap(compareByDescending { it })


And for your case:



val comparator = compareBy<Pair<Double, Int>> { it.first }


Custom comparator:



class CustomComparator<T: Comparable<T>> : Comparator<T> {

    override fun compare(o1: T, o2: T): Int {

        return o1.compareTo(o2)

    }

}





share|improve this answer























  • That's good, but I wanted for some implementation of generic class which can be used, for example, both for Pair<Int, String> and for Pair<Long, Double>
    – Alex Row
    Nov 22 at 21:46










  • Why compareBy and other helper functions don't work for you? You can use it to create Comparator of any Pairs.
    – Sergey
    Nov 23 at 7:54



















0














You can use the following function to combine two comparators into a pair comparator which compares the first value of a pair with the first comparator and then the second value with the second comparator:



fun <T, U> pairComparator(

    firstComparator: Comparator<T>, 

    secondComparator: Comparator<U>

): Comparator<Pair<T, U>> = 

         compareBy(firstComparator) { p: Pair<T, U> -> p.first }

          .thenBy(secondComparator) { p: Pair<T, U> -> p.second }


Then you use it as following:



val source = listOf(1 to 2.3, 1 to 2.0, 0 to 3.0)

val result1 = source.sortedWith(pairComparator(naturalOrder(), naturalOrder()))

println(result1)  // [(0, 3.0), (1, 2.0), (1, 2.3)]



val result2 = source.sortedWith(pairComparator(naturalOrder(), reverseOrder()))

println(result2)  // [(0, 3.0), (1, 2.3), (1, 2.0)]


See the full code here: https://pl.kotl.in/BkMOzb8CX






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    2 Answers
    2






    active

    oldest

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    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    1














    You can create comparator, using helping functions - compareBy, compareByDescending, naturalOrder, reverseOrder https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/index.html



    For example:



    val map = mapOf<Int, String>()
    
// ... add values to the map
    
val sortedMap: SortedMap<Int, String> = map.toSortedMap(compareByDescending { it })


    And for your case:



    val comparator = compareBy<Pair<Double, Int>> { it.first }


    Custom comparator:



    class CustomComparator<T: Comparable<T>> : Comparator<T> {
    
    override fun compare(o1: T, o2: T): Int {
    
        return o1.compareTo(o2)
    
    }
    
}





    share|improve this answer























    • That's good, but I wanted for some implementation of generic class which can be used, for example, both for Pair<Int, String> and for Pair<Long, Double>
      – Alex Row
      Nov 22 at 21:46










    • Why compareBy and other helper functions don't work for you? You can use it to create Comparator of any Pairs.
      – Sergey
      Nov 23 at 7:54
















    1














    You can create comparator, using helping functions - compareBy, compareByDescending, naturalOrder, reverseOrder https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/index.html



    For example:



    val map = mapOf<Int, String>()
    
// ... add values to the map
    
val sortedMap: SortedMap<Int, String> = map.toSortedMap(compareByDescending { it })


    And for your case:



    val comparator = compareBy<Pair<Double, Int>> { it.first }


    Custom comparator:



    class CustomComparator<T: Comparable<T>> : Comparator<T> {
    
    override fun compare(o1: T, o2: T): Int {
    
        return o1.compareTo(o2)
    
    }
    
}





    share|improve this answer























    • That's good, but I wanted for some implementation of generic class which can be used, for example, both for Pair<Int, String> and for Pair<Long, Double>
      – Alex Row
      Nov 22 at 21:46










    • Why compareBy and other helper functions don't work for you? You can use it to create Comparator of any Pairs.
      – Sergey
      Nov 23 at 7:54














    1












    1








    1






    You can create comparator, using helping functions - compareBy, compareByDescending, naturalOrder, reverseOrder https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/index.html



    For example:



    val map = mapOf<Int, String>()
    
// ... add values to the map
    
val sortedMap: SortedMap<Int, String> = map.toSortedMap(compareByDescending { it })


    And for your case:



    val comparator = compareBy<Pair<Double, Int>> { it.first }


    Custom comparator:



    class CustomComparator<T: Comparable<T>> : Comparator<T> {
    
    override fun compare(o1: T, o2: T): Int {
    
        return o1.compareTo(o2)
    
    }
    
}





    share|improve this answer














    You can create comparator, using helping functions - compareBy, compareByDescending, naturalOrder, reverseOrder https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.comparisons/index.html



    For example:



    val map = mapOf<Int, String>()
    
// ... add values to the map
    
val sortedMap: SortedMap<Int, String> = map.toSortedMap(compareByDescending { it })


    And for your case:



    val comparator = compareBy<Pair<Double, Int>> { it.first }


    Custom comparator:



    class CustomComparator<T: Comparable<T>> : Comparator<T> {
    
    override fun compare(o1: T, o2: T): Int {
    
        return o1.compareTo(o2)
    
    }
    
}






    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited Nov 22 at 20:21

























    answered Nov 22 at 20:02









    Sergey

    1,97621324




    1,97621324












    • That's good, but I wanted for some implementation of generic class which can be used, for example, both for Pair<Int, String> and for Pair<Long, Double>
      – Alex Row
      Nov 22 at 21:46










    • Why compareBy and other helper functions don't work for you? You can use it to create Comparator of any Pairs.
      – Sergey
      Nov 23 at 7:54


















    • That's good, but I wanted for some implementation of generic class which can be used, for example, both for Pair<Int, String> and for Pair<Long, Double>
      – Alex Row
      Nov 22 at 21:46










    • Why compareBy and other helper functions don't work for you? You can use it to create Comparator of any Pairs.
      – Sergey
      Nov 23 at 7:54
















    That's good, but I wanted for some implementation of generic class which can be used, for example, both for Pair<Int, String> and for Pair<Long, Double>
    – Alex Row
    Nov 22 at 21:46




    That's good, but I wanted for some implementation of generic class which can be used, for example, both for Pair<Int, String> and for Pair<Long, Double>
    – Alex Row
    Nov 22 at 21:46












    Why compareBy and other helper functions don't work for you? You can use it to create Comparator of any Pairs.
    – Sergey
    Nov 23 at 7:54




    Why compareBy and other helper functions don't work for you? You can use it to create Comparator of any Pairs.
    – Sergey
    Nov 23 at 7:54













    0














    You can use the following function to combine two comparators into a pair comparator which compares the first value of a pair with the first comparator and then the second value with the second comparator:



    fun <T, U> pairComparator(
    
    firstComparator: Comparator<T>, 
    
    secondComparator: Comparator<U>
    
): Comparator<Pair<T, U>> = 
    
         compareBy(firstComparator) { p: Pair<T, U> -> p.first }
    
          .thenBy(secondComparator) { p: Pair<T, U> -> p.second }


    Then you use it as following:



    val source = listOf(1 to 2.3, 1 to 2.0, 0 to 3.0)
    
val result1 = source.sortedWith(pairComparator(naturalOrder(), naturalOrder()))
    
println(result1)  // [(0, 3.0), (1, 2.0), (1, 2.3)]
    

    
val result2 = source.sortedWith(pairComparator(naturalOrder(), reverseOrder()))
    
println(result2)  // [(0, 3.0), (1, 2.3), (1, 2.0)]


    See the full code here: https://pl.kotl.in/BkMOzb8CX






    share|improve this answer


























      0














      You can use the following function to combine two comparators into a pair comparator which compares the first value of a pair with the first comparator and then the second value with the second comparator:



      fun <T, U> pairComparator(
      
    firstComparator: Comparator<T>, 
      
    secondComparator: Comparator<U>
      
): Comparator<Pair<T, U>> = 
      
         compareBy(firstComparator) { p: Pair<T, U> -> p.first }
      
          .thenBy(secondComparator) { p: Pair<T, U> -> p.second }


      Then you use it as following:



      val source = listOf(1 to 2.3, 1 to 2.0, 0 to 3.0)
      
val result1 = source.sortedWith(pairComparator(naturalOrder(), naturalOrder()))
      
println(result1)  // [(0, 3.0), (1, 2.0), (1, 2.3)]
      

      
val result2 = source.sortedWith(pairComparator(naturalOrder(), reverseOrder()))
      
println(result2)  // [(0, 3.0), (1, 2.3), (1, 2.0)]


      See the full code here: https://pl.kotl.in/BkMOzb8CX






      share|improve this answer
























        0












        0








        0






        You can use the following function to combine two comparators into a pair comparator which compares the first value of a pair with the first comparator and then the second value with the second comparator:



        fun <T, U> pairComparator(
        
    firstComparator: Comparator<T>, 
        
    secondComparator: Comparator<U>
        
): Comparator<Pair<T, U>> = 
        
         compareBy(firstComparator) { p: Pair<T, U> -> p.first }
        
          .thenBy(secondComparator) { p: Pair<T, U> -> p.second }


        Then you use it as following:



        val source = listOf(1 to 2.3, 1 to 2.0, 0 to 3.0)
        
val result1 = source.sortedWith(pairComparator(naturalOrder(), naturalOrder()))
        
println(result1)  // [(0, 3.0), (1, 2.0), (1, 2.3)]
        

        
val result2 = source.sortedWith(pairComparator(naturalOrder(), reverseOrder()))
        
println(result2)  // [(0, 3.0), (1, 2.3), (1, 2.0)]


        See the full code here: https://pl.kotl.in/BkMOzb8CX






        share|improve this answer












        You can use the following function to combine two comparators into a pair comparator which compares the first value of a pair with the first comparator and then the second value with the second comparator:



        fun <T, U> pairComparator(
        
    firstComparator: Comparator<T>, 
        
    secondComparator: Comparator<U>
        
): Comparator<Pair<T, U>> = 
        
         compareBy(firstComparator) { p: Pair<T, U> -> p.first }
        
          .thenBy(secondComparator) { p: Pair<T, U> -> p.second }


        Then you use it as following:



        val source = listOf(1 to 2.3, 1 to 2.0, 0 to 3.0)
        
val result1 = source.sortedWith(pairComparator(naturalOrder(), naturalOrder()))
        
println(result1)  // [(0, 3.0), (1, 2.0), (1, 2.3)]
        

        
val result2 = source.sortedWith(pairComparator(naturalOrder(), reverseOrder()))
        
println(result2)  // [(0, 3.0), (1, 2.3), (1, 2.0)]


        See the full code here: https://pl.kotl.in/BkMOzb8CX







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Nov 23 at 22:43









        Ilya

        8,96943056




        8,96943056






























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