How to Create a Map of Maps in Kotlin

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,

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")
        }
    }
}

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

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,

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")
        }
    }
}

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

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,

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")
        }
    }
}

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