Dart Map map()
Syntax & Examples

Syntax of Map.map()

The syntax of Map.map() method is:

 Map<K2, V2> map<K2, V2>(MapEntry<K2, V2> convert(K key, V value))

This map() method of Map returns a new map where all entries of this map are transformed by the given convert function.

Parameters

ParameterOptional/RequiredDescription
convertrequiredthe function used to transform entries of the map

Return Type

Map.map() returns value of type Map<K2, V2>.


✐ Examples

1 Convert scores to grades

In this example,

  1. We create a map scores with names as keys and scores as values.
  2. We then use the map() method to transform each entry by dividing the score by 10.0, effectively converting scores to grades.
  3. The transformed map grades is printed, showing the grades corresponding to each name.

Dart Program

void main() {
  Map<String, int> scores = {'Alice': 100, 'Bob': 80, 'Charlie': 90};
  Map<String, double> grades = scores.map((key, value) => MapEntry(key, value / 10.0));
  print(grades); // Output: {Alice: 10.0, Bob: 8.0, Charlie: 9.0}
}

Output

{Alice: 10.0, Bob: 8.0, Charlie: 9.0}

2 Map keys to their lengths

In this example,

  1. We create a map map with integers as keys and strings as values.
  2. We then use the map() method to transform each entry by mapping keys to the lengths of their corresponding values.
  3. The transformed map lengths is printed, showing the lengths corresponding to each key.

Dart Program

void main() {
  Map<int, String> map = {1: 'One', 2: 'Two', 3: 'Three'};
  Map<int, int> lengths = map.map((key, value) => MapEntry(key, value.length));
  print(lengths); // Output: {1: 3, 2: 3, 3: 5}
}

Output

{1: 3, 2: 3, 3: 5}

3 Map strings to their lengths

In this example,

  1. We create a map words with strings as keys and colors as values.
  2. We then use the map() method to transform each entry by mapping keys to the lengths of their corresponding values.
  3. The transformed map lengths is printed, showing the lengths corresponding to each key.

Dart Program

void main() {
  Map<String, String> words = {'apple': 'red', 'banana': 'yellow', 'cherry': 'red'};
  Map<String, int> lengths = words.map((key, value) => MapEntry(key, value.length));
  print(lengths); // Output: {apple: 3, banana: 6, cherry: 3}
}

Output

{apple: 3, banana: 6, cherry: 3}

Summary

In this Dart tutorial, we learned about map() method of Map: the syntax and few working examples with output and detailed explanation for each example.