Easy way to negate a predicate (e.g. (String) -> Boolean)) in Kotlin

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Easy way to negate a predicate (e.g. (String) -> Boolean)) in Kotlin



Given a predicate (String) -> Boolean I wondered whether there is an easy way to negate the outcome of that predicate.
As long as I use a list, I can simply switch from filter to filterNot, but what if I have, lets say... a Map and use filterKeys?


(String) -> Boolean


filter


filterNot


Map


filterKeys



What I used so far is:


val myPredicate : (String) -> Boolean = TODO()
val map : Map<String, String> = TODO()

map.filterKeys !myPredicate(it)



But I wonder why there is an overloaded function for List, but not for Map. Moreover I also wonder, why there isn't something similar to what we have in Java, i.e. Predicate.negate() and since Java 11 Predicate.not(..).


List


Map


Predicate.negate()


Predicate.not(..)



Or does it exist and I just haven't found it?





There is filterNot for Map as well: kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/…
– msrd0
yesterday


filterNot


Map





ok... I specifically meant filterKeys and filterValues but also any other function accepting a ~predicate.. Do there exist any easy convenience methods as the ones shown in the question? If not would be interesting why...
– Roland
yesterday



filterKeys


filterValues





Actually this is a really interesting question. It might be a performance issue (or I was just not able to figure it out): stackoverflow.com/q/52057967/3755692
– msrd0
yesterday









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