Kotlin - how to find number of repeated values in a list?

问题

I have a list, e.g like:

val list = listOf("orange", "apple", "apple", "banana", "water", "bread", "banana")

How can i check how many times apple is duplicated in this list?

回答1:

list.count { it == "apple" }

Documentation: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-list/, https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/count.html

回答2:

One way to find all the repeated values in a list is using groupingBy and then filter the values which are > 1. E.g.

val list = listOf("orange", "apple", "apple", "banana", "water", "bread", "banana")
println(list.groupingBy { it }.eachCount().filter { it.value > 1 })

Output

{apple=2, banana=2}

来源：https://stackoverflow.com/questions/47200440/kotlin-how-to-find-number-of-repeated-values-in-a-list