Remove null values from a map in Kotlin

This article explores different ways to remove null values from a map in Kotlin.

1. Using `remove()` function

To remove all occurrences of null values from the map, you can continuously call remove(null) on the collection returned by values property until all nulls are removed.

fun main() {

val map: MutableMap<String, String?> = HashMap()

map["RED"] = "#FF0000"

map["GREY"] = null

map["BLUE"] = "#0000FF"

map["YELLOW"] = null

while (map.values.remove(null)) {}

println(map) // {RED=#FF0000, BLUE=#0000FF}

}

Download Code

2. Using `removeAll()` function

The removeAll() function removes all elements contained in the specified collection. To remove all occurrences of null values from the map, you can pass a singleton sequence containing only null.

fun main() {

val map: MutableMap<String, String?> = HashMap()

map["RED"] = "#FF0000"

map["GREY"] = null

map["BLUE"] = "#0000FF"

map["YELLOW"] = null

map.values.removeAll(sequenceOf(null))

println(map) // {RED=#FF0000, BLUE=#0000FF}

}

Download Code

3. Using `removeIf()` function

To filter null values from the map, you can use the removeIf() function. It removes all key/value pairs from the map that satisfy the given predicate.

fun main() {

val map: MutableMap<String, String?> = HashMap()

map["RED"] = "#FF0000"

map["GREY"] = null

map["BLUE"] = "#0000FF"

map["YELLOW"] = null

map.values.removeIf { it == null }

println(map) // {RED=#FF0000, BLUE=#0000FF}

}

Download Code

4. Using Iterator

Another plausible way of iteration is using an iterator. The following code example demonstrates its usage to remove all key/value pairs with null values.

fun <K, V> removeNulls(map: MutableMap<K, V?>) {

val itr = map.entries.iterator()

while (itr.hasNext())

{

val curr = itr.next()

if (curr.value == null) itr.remove()

}

fun main() {

val map: MutableMap<String, String?> = HashMap()

map["RED"] = "#FF0000"

map["GREY"] = null

map["BLUE"] = "#0000FF"

map["YELLOW"] = null

removeNulls<String, String?>(map)

println(map) // {RED=#FF0000, BLUE=#0000FF}

}

Download Code

That’s all about removing null values from a map in Kotlin.

Remove null values from a map in Kotlin

1. Using remove() function

2. Using removeAll() function

3. Using removeIf() function

4. Using Iterator

Share this:

1. Using `remove()` function

2. Using `removeAll()` function

3. Using `removeIf()` function