Dart map function

last modified January 28, 2024

In this article we show how to map elements of an Iterable to a function in Dart language. In our examples, we use the list collection.

The map function returns a lazy Iterable which is created by calling the specified function on each element of an Iterable.

Dart map simple example

The following is a simple map function example.

main.dart

void main() { final vals = [1, 2, 3, 4, 5, 6];

final res = vals.map((e) => e * 5); print(res); print(res.toList()); }

We have a list of integers. We apply the map function on each of the elements. The function is a lambda expression, which multiplies an element by 5.

$ dart main.dart (5, 10, 15, 20, 25, 30) [5, 10, 15, 20, 25, 30]

Dart map example II

In the following example, we apply the map function on a list of words.

main.dart

void main() { final words = [‘sky’, ‘cloud’, ‘snow’, ‘summer’, ‘cup’, ‘water’];

final wlns = words.map((e) => e.length); print(wlns); }

In the program, we transform a list of words into a sequence of word lengths.

$ dart main.dart (3, 5, 4, 6, 3, 5)

Dart indexed map function

If we want to work with element indexes, we can use the mapIndexed function, which is available in the collection library.

$ dart pub add collection

We add the library to the project.

main.dart

import ‘package:collection/collection.dart’;

void main() { final words = [‘sky’, ‘cloud’, ‘snow’, ‘summer’, ‘cup’, ‘water’];

final wlns = words.mapIndexed((idx, word) => “{idx=$idx, len=${word.length}}”); print(wlns); }

We map the list elements into a iterable of strings, which contain the index value and the string length.

$ dart main.dart ({idx=0, len=3}, {idx=1, len=5}, {idx=2, len=4}, …

Dart map projection

A projection is a selection of specific fields from the returned objects.

main.dart

class User { final String name; final String occupation; final int salary;

User(this.name, this.occupation, this.salary);

@override String toString() { return “$name|$occupation|$salary”; } }

void main() { final users = <User>[ User(“John”, “Doe”, 1230), User(“Lucy”, “Novak”, 670), User(“Ben”, “Walter”, 2050), User(“Robin”, “Brown”, 2300), User(“Amy”, “Doe”, 1250), User(“Joe”, “Draker”, 1190), User(“Janet”, “Doe”, 980), User(“Albert”, “Novak”, 1930), ];

final salaries = users.map((e) => e.salary); print(salaries); }

We have list of users having three fields: first name, last name, and salary. We pick the salary field to form a new lazy iterable.

$ dart main.dart (1230, 670, 2050, 2300, 1250, 1190, 980, 1930)

Source

Dart map method - language reference

In this article we have have called the map function on elements of a list collection.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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