Filtering and Mapping Collections in Dart

In Dart, you can easily manipulate collections such as List and Set using the where method for filtering and the map method for transforming elements. These methods provide a functional programming style that enhances code readability and maintainability.

1. Filtering Collections with where

The where method is used to filter elements in a collection based on a specified condition. It returns a new iterable containing only the elements that satisfy the condition defined in the provided function.

Example of Filtering a List

void main() {
    List<int> numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

    // Filtering even numbers
    Iterable<int> evenNumbers = numbers.where((number) => number.isEven);

    // Printing the filtered list
    print('Even numbers: $evenNumbers'); // Output: Even numbers: (2, 4, 6, 8, 10)
}
</int></int>

In this example, we create a list of integers and use the where method to filter out even numbers. The condition is defined in the lambda function, which checks if each number is even. The result is an iterable containing only the even numbers.

2. Mapping Collections with map

The map method is used to transform each element in a collection by applying a specified function. It returns a new iterable containing the results of applying the function to each element in the original collection.

Example of Mapping a List

void main() {
    List<int> numbers = [1, 2, 3, 4, 5];

    // Mapping to square each number
    Iterable<int> squaredNumbers = numbers.map((number) => number * number);

    // Printing the mapped list
    print('Squared numbers: $squaredNumbers'); // Output: Squared numbers: (1, 4, 9, 16, 25)
}
</int></int>

In this example, we create a list of integers and use the map method to square each number. The transformation is defined in the lambda function, which multiplies each number by itself. The result is an iterable containing the squared values.

3. Chaining where and map

You can also chain the where and map methods to perform filtering and mapping in a single expression. This allows for concise and expressive code.

Example of Chaining where and map

void main() {
    List<int> numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

    // Filtering even numbers and then mapping to square them
    Iterable<int> squaredEvenNumbers = numbers
        .where((number) => number.isEven)
        .map((number) => number * number);

    // Printing the result
    print('Squared even numbers: $squaredEvenNumbers'); // Output: Squared even numbers: (4, 16, 36, 64, 100)
}
</int></int>

In this example, we first filter the even numbers from the list and then square each of those numbers in a single expression. The result is an iterable containing the squared values of the even numbers.

4. Conclusion

Filtering and mapping collections in Dart using the where and map methods provide a powerful and expressive way to manipulate data. These methods enhance code readability and allow for functional programming patterns, making it easier to work with collections in Dart applications.