kotlin-stdlib/kotlin.comparisons/compareValuesBy

compareValuesBy

fun <T> compareValuesBy(a: T, b: T, vararg selectors: (T) -> Comparable<*>?): Int(source)

Compares two values using the specified functions selectors to calculate the result of the comparison. The functions are called sequentially, receive the given values a and b and return Comparable objects. As soon as the Comparable instances returned by a function for a and b values do not compare as equal, the result of that comparison is returned.

Since Kotlin

1.0

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   fun compareLengthThenString(a: String, b: String): Int =
    compareValuesBy(a, b, { it.length }, { it })

println("compareLengthThenString(\"b\", \"aa\") < 0 is ${compareLengthThenString("b", "aa") < 0}") // true

println("compareLengthThenString(\"a\", \"b\") < 0 is ${compareLengthThenString("a", "b") < 0}") // true
println("compareLengthThenString(\"b\", \"a\") > 0 is ${compareLengthThenString("b", "a") > 0}") // true
println("compareLengthThenString(\"a\", \"a\") == 0 is ${compareLengthThenString("a", "a") == 0}") // true 
   //sampleEnd
}
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fun compareLengthThenString(a: String, b: String): Int =
    compareValuesBy(a, b, { it.length }, { it })
println("compareLengthThenString(\"b\", \"aa\") < 0 is ${compareLengthThenString("b", "aa") < 0}") // true
println("compareLengthThenString(\"a\", \"b\") < 0 is ${compareLengthThenString("a", "b") < 0}") // true
println("compareLengthThenString(\"b\", \"a\") > 0 is ${compareLengthThenString("b", "a") > 0}") // true
println("compareLengthThenString(\"a\", \"a\") == 0 is ${compareLengthThenString("a", "a") == 0}") // true 
Open in Playground →
Target: JVMRunning on v.2.1.20

inline fun <T> compareValuesBy(a: T, b: T, selector: (T) -> Comparable<*>?): Int(source)

Compares two values using the specified selector function to calculate the result of the comparison. The function is applied to the given values a and b and return Comparable objects. The result of comparison of these Comparable instances is returned.

Since Kotlin

1.0

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   fun compareLength(a: String, b: String): Int =
    compareValuesBy(a, b) { it.length }

println("compareLength(\"a\", \"b\") == 0 is ${compareLength("a", "b") == 0}") // true
println("compareLength(\"bb\", \"a\") > 0 is ${compareLength("bb", "a") > 0}") // true
println("compareLength(\"a\", \"bb\") < 0 is ${compareLength("a", "bb") < 0}") // true 
   //sampleEnd
}
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fun compareLength(a: String, b: String): Int =
    compareValuesBy(a, b) { it.length }
println("compareLength(\"a\", \"b\") == 0 is ${compareLength("a", "b") == 0}") // true
println("compareLength(\"bb\", \"a\") > 0 is ${compareLength("bb", "a") > 0}") // true
println("compareLength(\"a\", \"bb\") < 0 is ${compareLength("a", "bb") < 0}") // true 
Open in Playground →
Target: JVMRunning on v.2.1.20

inline fun <T, K> compareValuesBy(a: T, b: T, comparator: Comparator<in K>, selector: (T) -> K): Int(source)

Compares two values using the specified selector function to calculate the result of the comparison. The function is applied to the given values a and b and return objects of type K which are then being compared with the given comparator.

Since Kotlin

1.0

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   fun compareInsensitiveOrder(a: Char, b: Char): Int =
    compareValuesBy(a, b, String.CASE_INSENSITIVE_ORDER, { c -> c.toString() })

println("compareInsensitiveOrder('a', 'a') == 0 is ${compareInsensitiveOrder('a', 'a') == 0}") // true
println("compareInsensitiveOrder('a', 'A') == 0 is ${compareInsensitiveOrder('a', 'A') == 0}") // true

println("compareInsensitiveOrder('a', 'b') < 0 is ${compareInsensitiveOrder('a', 'b') < 0}") // true
println("compareInsensitiveOrder('A', 'b') < 0 is ${compareInsensitiveOrder('A', 'b') < 0}") // true
println("compareInsensitiveOrder('b', 'a') > 0 is ${compareInsensitiveOrder('b', 'a') > 0}") // true 
   //sampleEnd
}
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fun compareInsensitiveOrder(a: Char, b: Char): Int =
    compareValuesBy(a, b, String.CASE_INSENSITIVE_ORDER, { c -> c.toString() })
println("compareInsensitiveOrder('a', 'a') == 0 is ${compareInsensitiveOrder('a', 'a') == 0}") // true
println("compareInsensitiveOrder('a', 'A') == 0 is ${compareInsensitiveOrder('a', 'A') == 0}") // true
println("compareInsensitiveOrder('a', 'b') < 0 is ${compareInsensitiveOrder('a', 'b') < 0}") // true
println("compareInsensitiveOrder('A', 'b') < 0 is ${compareInsensitiveOrder('A', 'b') < 0}") // true
println("compareInsensitiveOrder('b', 'a') > 0 is ${compareInsensitiveOrder('b', 'a') > 0}") // true 
Open in Playground →
Target: JVMRunning on v.2.1.20

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