Dart Set retainWhere()
Syntax & Examples

Set.retainWhere() method

The `retainWhere` method in Dart removes all elements from the set that fail to satisfy a given test.

Syntax of Set.retainWhere()

The syntax of Set.retainWhere() method is:

 void retainWhere(bool test(E element))

This retainWhere() method of Set removes all elements of this set that fail to satisfy test.

Parameters

ParameterOptional/RequiredDescription
testrequiredA function that takes an element of the set as input and returns a boolean value. If the return value is false, the element is removed from the set.

Return Type

Set.retainWhere() returns value of type void.


✐ Examples

1 Retain even numbers in set

In this example,

  1. We create a Set set containing integers.
  2. We use the retainWhere() method with a test function that retains only even numbers.
  3. We print the resulting Set to standard output.

Dart Program

void main() {
  Set<int> set = {1, 2, 3, 4};
  set.retainWhere((element) => element % 2 == 0);
  print('Set after retaining even numbers: $set');
}

Output

Set after retaining even numbers: {2, 4}

2 Retain strings with length greater than 5 in set

In this example,

  1. We create a Set set containing strings.
  2. We use the retainWhere() method with a test function that retains only strings with a length greater than 5.
  3. We print the resulting Set to standard output.

Dart Program

void main() {
  Set<String> set = {'apple', 'banana', 'orange', 'grape'};
  set.retainWhere((element) => element.length > 5);
  print('Set after retaining strings with length greater than 5: $set');
}

Output

Set after retaining strings with length greater than 5: {banana, orange}

Summary

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