Dart Runes expand()
Syntax & Examples

Runes.expand() method

The `expand` method in Dart expands each element of the Iterable into zero or more elements.

Syntax of Runes.expand()

The syntax of Runes.expand() method is:

 Iterable<T> expand<T>(Iterable<T> f(int element))

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

Parameters

ParameterOptional/RequiredDescription
frequiredA function that takes an element of the Iterable and returns an Iterable.

Return Type

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


✐ Examples

1 Expanding elements in a list of numbers

In this example,

  1. We create a list numbers containing integers.
  2. We use the expand() method with a function that returns the element and the element plus one.
  3. We convert the expanded iterable to a list and print it to standard output.

Dart Program

void main() {
  List<int> numbers = [1, 2, 3];
  Iterable<int> expanded = numbers.expand((element) => [element, element + 1]);
  print(expanded.toList());
}

Output

[1, 2, 2, 3, 3, 4]

2 Expanding elements in a list of strings

In this example,

  1. We create a list words containing strings.
  2. We use the expand() method with a function that returns the uppercase and lowercase versions of each word.
  3. We convert the expanded iterable to a list and print it to standard output.

Dart Program

void main() {
  List<String> words = ['hello', 'world'];
  Iterable<String> expanded = words.expand((word) => [word.toUpperCase(), word.toLowerCase()]);
  print(expanded.toList());
}

Output

[HELLO, hello, WORLD, world]

3 Expanding elements in a set of numbers

In this example,

  1. We create a set uniqueNumbers containing integers.
  2. We use the expand() method with a function that returns the number and the number multiplied by two.
  3. We convert the expanded iterable to a list and print it to standard output.

Dart Program

void main() {
  Set<int> uniqueNumbers = {1, 2, 3};
  Iterable<int> expanded = uniqueNumbers.expand((number) => [number, number * 2]);
  print(expanded.toList());
}

Output

[1, 2, 2, 4, 3, 6]

Summary

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