Dart .map()

In Dart, the .map() method creates a new map by transforming each key–value pair of an existing map using a provided function.

Syntax

myMap.map((key, value) => MapEntry(newKey, newValue))

Here, myMap is the map whose entries are to be transformed.

Parameters:

• A function that takes two arguments:
  • key: The key from the original map.
  • value: The value associated with that key.
• The function must return a MapEntry, which defines the key–value pair in the new map.

Return value:

The .map() method returns a new Map containing the transformed key–value pairs.

Note: The original map remains unchanged.

Example 1

In the following example, the .map() method is used to create a new map by increasing each value by 1:

void main() {
  Map<String, int> myMap = {
    'a': 1,
    'b': 2,
    'c': 3
  };

  print('Original Map: $myMap');

  // Using .map() to increase each value by 1
  Map<String, int> newMap = myMap.map(
    (key, value) => MapEntry(key, value + 1)
  );

  print('New Map after using .map(): $newMap');
}

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Here is the output for the above example:

Original Map: {a: 1, b: 2, c: 3}
New Map after using .map(): {a: 2, b: 3, c: 4}

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Example 2

In the following example, the .map() method is used to convert all values in a map to uppercase:

void main() {
  Map<String, String> myMap = {
    'x': 'apple',
    'y': 'banana',
    'z': 'cherry'
  };

  print('Original Map: $myMap');

  // Using .map() to convert values to uppercase
  Map<String, String> newMap = myMap.map(
    (key, value) => MapEntry(key, value.toUpperCase())
  );

  print('New Map after using .map(): $newMap');
}

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Here is the output for the above example:

Original Map: {x: apple, y: banana, z: cherry}
New Map after using .map(): {x: APPLE, y: BANANA, z: CHERRY}

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