How to Create a Map of Maps in Dart

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

For example,

void main() {
  // Declare a map of maps
  Map<int, Map<int, int>> outerMap = {};

  // Populate the inner maps
  Map<int, int> innerMap1 = {1: 10, 2: 20, 3: 30};
  Map<int, int> innerMap2 = {4: 40, 5: 50, 6: 60};

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

  // Print the resulting map of maps
  print('Map of maps with integer keys and values:');
  outerMap.forEach((outerKey, innerMap) {
    print('Outer key: $outerKey');
    innerMap.forEach((innerKey, value) {
      print('  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 Dart by using the Map data structure. 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,

void main() {
  // Declare a map of maps
  Map<String, Map<int, String>> outerMap = {};

  // Populate the inner maps
  Map<int, String> innerMap1 = {1: 'one', 2: 'two', 3: 'three'};
  Map<int, String> innerMap2 = {4: 'four', 5: 'five', 6: 'six'};

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

  // Print the resulting map of maps
  print('Map of maps with mixed key and value types:');
  outerMap.forEach((outerKey, innerMap) {
    print('Outer key: $outerKey');
    innerMap.forEach((innerKey, value) {
      print('  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 Dart by using the Map data structure. This example demonstrates creating a map where both the outer and inner maps use strings for keys and doubles for values.

For example,

void main() {
  // Declare a map of maps
  Map<String, Map<String, double>> outerMap = {};

  // Populate the inner maps
  Map<String, double> innerMap1 = {'A': 1.1, 'B': 2.2, 'C': 3.3};
  Map<String, double> innerMap2 = {'D': 4.4, 'E': 5.5, 'F': 6.6};

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

  // Print the resulting map of maps
  print('Map of maps with string keys and double values:');
  outerMap.forEach((outerKey, innerMap) {
    print('Outer key: $outerKey');
    innerMap.forEach((innerKey, value) {
      print('  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