How to Create a Map of Maps in Kotlin - Step by Step Examples

How to Create a Map of Maps in Kotlin ?

Answer

To create a map of maps in Kotlin, you can use the Map and MutableMap data structures. A map of maps allows you to organize data hierarchically, where each key in the outer map points to another map.

✐ Examples

1 Creating a Map of Maps with Integer Keys and Values

We can create a map of maps in Kotlin by using the Map and MutableMap data structures. This example demonstrates creating a map where both the outer and inner maps use integers for keys and values.

For example,

We start by declaring and initializing a mutable map named outerMap where each value is another mutable map.
We populate the inner maps with key-value pairs.
We insert the inner maps into the outer map using appropriate keys.
We print the resulting map of maps to the console to verify the structure.

Kotlin Program

fun main() {
    // Declare a map of maps
    val outerMap: MutableMap<Int, MutableMap<Int, Int>> = mutableMapOf()

    // Populate the inner maps
    val innerMap1 = mutableMapOf(1 to 10, 2 to 20, 3 to 30)
    val innerMap2 = mutableMapOf(4 to 40, 5 to 50, 6 to 60)

    // Insert the inner maps into the outer map
    outerMap[1] = innerMap1
    outerMap[2] = innerMap2

    // Print the resulting map of maps
    println("Map of maps with integer keys and values:")
    for ((outerKey, innerMap) in outerMap) {
        println("Outer key: $outerKey")
        for ((innerKey, value) in innerMap) {
            println("  Inner key: $innerKey, value: $value")
        }
    }
}

Output

Map of maps with integer keys and values:
Outer key: 1
  Inner key: 1, value: 10
  Inner key: 2, value: 20
  Inner key: 3, value: 30
Outer key: 2
  Inner key: 4, value: 40
  Inner key: 5, value: 50
  Inner key: 6, value: 60

2 Creating a Map of Maps with Mixed Key and Value Types

We can create a map of maps in Kotlin by using the Map and MutableMap data structures. This example demonstrates creating a map where the outer map uses strings for keys and the inner maps use integers for keys and strings for values.

For example,

We start by declaring and initializing a mutable map named outerMap where each value is another mutable map with mixed key and value types.
We populate the inner maps with key-value pairs.
We insert the inner maps into the outer map using appropriate keys.
We print the resulting map of maps to the console to verify the structure.

Kotlin Program

fun main() {
    // Declare a map of maps
    val outerMap: MutableMap<String, MutableMap<Int, String>> = mutableMapOf()

    // Populate the inner maps
    val innerMap1 = mutableMapOf(1 to "one", 2 to "two", 3 to "three")
    val innerMap2 = mutableMapOf(4 to "four", 5 to "five", 6 to "six")

    // Insert the inner maps into the outer map
    outerMap["first"] = innerMap1
    outerMap["second"] = innerMap2

    // Print the resulting map of maps
    println("Map of maps with mixed key and value types:")
    for ((outerKey, innerMap) in outerMap) {
        println("Outer key: $outerKey")
        for ((innerKey, value) in innerMap) {
            println("  Inner key: $innerKey, value: $value")
        }
    }
}

Output

Map of maps with mixed key and value types:
Outer key: first
  Inner key: 1, value: one
  Inner key: 2, value: two
  Inner key: 3, value: three
Outer key: second
  Inner key: 4, value: four
  Inner key: 5, value: five
  Inner key: 6, value: six

3 Creating a Map of Maps with String Keys and Double Values

We can create a map of maps in Kotlin by using the Map and MutableMap data structures. This example demonstrates creating a map where both the outer and inner maps use strings for keys and doubles for values.

For example,

We start by declaring and initializing a mutable map named outerMap where each value is another mutable map with strings for keys and doubles for values.
We populate the inner maps with key-value pairs.
We insert the inner maps into the outer map using appropriate keys.
We print the resulting map of maps to the console to verify the structure.

Kotlin Program

fun main() {
    // Declare a map of maps
    val outerMap: MutableMap<String, MutableMap<String, Double>> = mutableMapOf()

    // Populate the inner maps
    val innerMap1 = mutableMapOf("A" to 1.1, "B" to 2.2, "C" to 3.3)
    val innerMap2 = mutableMapOf("D" to 4.4, "E" to 5.5, "F" to 6.6)

    // Insert the inner maps into the outer map
    outerMap["group1"] = innerMap1
    outerMap["group2"] = innerMap2

    // Print the resulting map of maps
    println("Map of maps with string keys and double values:")
    for ((outerKey, innerMap) in outerMap) {
        println("Outer key: $outerKey")
        for ((innerKey, value) in innerMap) {
            println("  Inner key: $innerKey, value: $value")
        }
    }
}

Output

Map of maps with string keys and double values:
Outer key: group1
  Inner key: A, value: 1.1
  Inner key: B, value: 2.2
  Inner key: C, value: 3.3
Outer key: group2
  Inner key: D, value: 4.4
  Inner key: E, value: 5.5
  Inner key: F, value: 6.6

Summary

In this tutorial, we learned How to Create a Map of Maps in Kotlin language with well detailed examples.

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How to Create a Map of Maps in Kotlin - Step by Step Examples