Kotlin Map filterNotTo()
Syntax & Examples

Syntax of Map.filterNotTo()

The syntax of Map.filterNotTo() extension function is:

fun <K, V, M : MutableMap<in K, in V>> Map<out K, V>.filterNotTo( destination: M, predicate: (Entry<K, V>) -> Boolean ): M

This filterNotTo() extension function of Map appends all entries not matching the given predicate into the given destination.

✐ Examples

1 Filter out key 'b' from the map

In this example,

We create a map named map1 with key-value pairs ('a' to 1), ('b' to 2), ('c' to 3).
We create an empty mutable map filteredMap1.
We use the filterNotTo() function on map1 to filter out key 'b' and append the remaining entries to filteredMap1.
The resulting filteredMap1 contains key-value pairs ('a' to 1), ('c' to 3).
We print filteredMap1 to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map1 = mapOf('a' to 1, 'b' to 2, 'c' to 3)
    val filteredMap1 = mutableMapOf<Char, Int>()
    map1.filterNotTo(filteredMap1) { (key, value) -> key == 'b' }
    println(filteredMap1)
}

Output

{a=1, c=3}

2 Filter out keys 'a' and 'c' from the map

In this example,

We create a map named map2 with key-value pairs ('a' to 1), ('b' to 2), ('c' to 3).
We create an empty mutable map filteredMap2.
We use the filterNotTo() function on map2 to filter out keys 'a' and 'c' and append the remaining entries to filteredMap2.
The resulting filteredMap2 contains key-value pairs ('b' to 2).
We print filteredMap2 to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map2 = mapOf('a' to 1, 'b' to 2, 'c' to 3)
    val filteredMap2 = mutableMapOf<Char, Int>()
    map2.filterNotTo(filteredMap2) { (key, value) -> key == 'a' || key == 'c' }
    println(filteredMap2)
}

Output

{b=2}

3 Filter out keys with length greater than 5 from the map

In this example,

We create a map named map3 with key-value pairs ('apple' to 1), ('banana' to 2), ('cherry' to 3).
We create an empty mutable map filteredMap3.
We use the filterNotTo() function on map3 to filter out keys with length greater than 5 and append the remaining entries to filteredMap3.
The resulting filteredMap3 contains key-value pairs ('apple' to 1).
We print filteredMap3 to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map3 = mapOf("apple" to 1, "banana" to 2, "cherry" to 3)
    val filteredMap3 = mutableMapOf<String, Int>()
    map3.filterNotTo(filteredMap3) { (key, value) -> key.length > 5 }
    println(filteredMap3)
}

Output

{apple=1}

Summary

In this Kotlin tutorial, we learned about filterNotTo() extension function of Map: the syntax and few working examples with output and detailed explanation for each example.