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How to convert a List to a Map in Kotlin?
In this article, we will see how we can convert a List to a Map using various options provided by the Kotlin Library.
Example: Using associate()
The most standard way of converting a list into a map is by using the associate() function. This function takes a list of items as an argument and it returns a map containing key-value pairs. In the following example, we will see how it works.
Example
data class mySubjectList(var name: String, var priority: String)
fun main() {
val mySubjectList: List<mySubjectList> = listOf(
mySubjectList("Java", "1"),
mySubjectList("Kotlin", "2"),
mySubjectList("C", "3")
)
// Creating a map and adding my own list of values in it.
val myMap: Map<String, String> = mySubjectList.associate {
Pair(it.priority, it.name)
}
println(myMap)
}Output
Once we run the above piece of code, it will generate the following output which is a map and we get the output in a key-value format.
{1=Java, 2=Kotlin, 3=C}Example: Using associateBy()
AssociateBy() is another function that can be used in order to transform a list into a Map. In the following example, we will see how we can implement the same.
Example
data class mySubjectList(var name: String, var priority: String)
fun main() {
val mySubjectList: List<mySubjectList> = listOf(
mySubjectList("Java", "1"),
mySubjectList("Kotlin", "2"),
mySubjectList("C", "3")
)
// Creating a map and adding my own list of the values in it
val myMap: Map<String, String> = mySubjectList.associateBy(
{it.priority}, {it.name}
)
println(myMap)
}Output
It will generate the following output which is a map and we get the output in a key-value format.
{1=Java, 2=Kotlin, 3=C}Example: Using toMap()
Kotlin library provides another function to convert a list of items into a Map. Kotlin Map class contains a function called toMap() which returns a new map containing all the key-value pairs from a given collection. Let's see how it works.
Example
data class mySubjectList(var name: String, var priority: String)
fun main() {
val mySubjectList: List<mySubjectList> = listOf(
mySubjectList("Java", "1"),
mySubjectList("Kotlin", "2"),
mySubjectList("C", "3")
)
// Creating a map and adding my own list of the values in it .
val myMap: Map<String, String> = mySubjectList.map{
it.priority to it.name
}.toMap()
println(myMap)
}Output
Once we run the above piece of code, it will generate the following output which is a map and we get the output in a key-value format.
{1=Java, 2=Kotlin, 3=C}
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