Dart List expand()
Syntax & Examples

Syntax of List.expand()

The syntax of List.expand() method is:

 Iterable<T> expand<T>(Iterable<T> toElements(E element))

This expand() method of List expands each element of this Iterable into zero or more elements.

Parameters

ParameterOptional/RequiredDescription
toElementsrequireda function that converts each element into zero or more elements

Return Type

List.expand() returns value of type Iterable<T>.


✐ Examples

1 Expand numbers in a list

In this example,

  1. We create a list named numbers containing integers.
  2. We use the expand() method with a function that duplicates each element and adds one to it.
  3. The resulting iterable contains the expanded numbers.
  4. We print the expanded numbers to standard output.

Dart Program

void main() {
  List<int> numbers = [1, 2, 3];
  Iterable<int> expandedNumbers = numbers.expand((element) => [element, element + 1]);
  print('Expanded numbers: $expandedNumbers');
}

Output

Expanded numbers: (1, 2, 2, 3, 3, 4)

2 Expand words in a list

In this example,

  1. We create a list named words containing strings.
  2. We use the expand() method with a function that splits each word into individual characters.
  3. The resulting iterable contains the expanded words.
  4. We print the expanded words to standard output.

Dart Program

void main() {
  List<String> words = ['hello', 'world'];
  Iterable<String> expandedWords = words.expand((element) => element.split(''));
  print('Expanded words: $expandedWords');
}

Output

Expanded words: (h, e, l, l, o, w, o, r, l, d)

3 Expand elements in a set

In this example,

  1. We create a set named set containing integers.
  2. We use the expand() method with a function that duplicates each element and multiplies it by two.
  3. The resulting iterable contains the expanded set elements.
  4. We print the expanded set elements to standard output.

Dart Program

void main() {
  Set<int> set = {1, 2, 3};
  Iterable<int> expandedSet = set.expand((element) => [element, element * 2]);
  print('Expanded set: $expandedSet');
}

Output

Expanded set: (1, 2, 2, 4, 3, 6)

Summary

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