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.
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.
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.
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.
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
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