Dart collections are a set of classes that provide data structures to store and manipulate groups of objects. Dart's core library provides several types of collections, including lists, sets, and maps. These collections are essential for managing and processing data efficiently in Dart programs.

Types of Dart Collections

List:
- An ordered collection of objects.
- Each element in a list is indexed, starting from 0.
- Dart provides List and its various implementations, such as List (growable list) and FixedLengthList.

    // Example of a List
    void main() {
      List<int> numbers = [1, 2, 3, 4, 5];
      print(numbers[0]); // Output: 1
      numbers.add(6);
      print(numbers);    // Output: [1, 2, 3, 4, 5, 6]
    }

Set:
- An unordered collection of unique items.
- It does not allow duplicate elements.
- Useful for operations that require uniqueness and set operations like union and intersection.

    // Example of a Set
    void main() {
      Set<String> fruits = {'apple', 'banana', 'orange'};
      fruits.add('apple'); // Duplicate element, will not be added
      print(fruits);       // Output: {apple, banana, orange}
    }

Map:
- A collection of key-value pairs, where each key is unique.
- Keys and values can be of any type.
- Provides fast lookup based on keys.

    // Example of a Map
    void main() {
      Map<String, int> ages = {
        'Alice': 25,
        'Bob': 30,
        'Charlie': 35
      };
      print(ages['Alice']); // Output: 25
      ages['Dave'] = 40;
      print(ages);          // Output: {Alice: 25, Bob: 30, Charlie: 35, Dave: 40}
    }

Common Collection Operations

Iteration:

  void main() {
    List<int> numbers = [1, 2, 3, 4, 5];
    for (int number in numbers) {
      print(number); // Output: 1 2 3 4 5
    }
  }

Filtering:

  void main() {
    List<int> numbers = [1, 2, 3, 4, 5];
    var evenNumbers = numbers.where((number) => number.isEven);
    print(evenNumbers.toList()); // Output: [2, 4]
  }

Mapping:

  void main() {
    List<int> numbers = [1, 2, 3, 4, 5];
    var squares = numbers.map((number) => number * number);
    print(squares.toList()); // Output: [1, 4, 9, 16, 25]
  }

Reducing:

  void main() {
    List<int> numbers = [1, 2, 3, 4, 5];
    var sum = numbers.reduce((a, b) => a + b);
    print(sum); // Output: 15
  }

Specialized Collections

Dart also provides specialized collections through the collection package, which includes more advanced data structures like:

Queue:
- An implementation of a double-ended queue.
- Supports adding and removing items from both ends.

    import 'dart:collection';

    void main() {
      Queue<int> queue = Queue();
      queue.addAll([1, 2, 3]);
      queue.addFirst(0);
      queue.addLast(4);
      print(queue); // Output: {0, 1, 2, 3, 4}
    }

LinkedHashMap:
- A hash map that maintains the insertion order of keys.

    import 'dart:collection';

    void main() {
      LinkedHashMap<String, int> map = LinkedHashMap();
      map['Alice'] = 25;
      map['Bob'] = 30;
      map['Charlie'] = 35;
      print(map); // Output: {Alice: 25, Bob: 30, Charlie: 35}
    }

Conclusion

Dart collections are essential tools for managing data in your Dart applications. They offer a variety of data structures that cater to different needs, from ordered lists to unique sets and key-value maps. Understanding and using these collections effectively can significantly enhance the performance and readability of your code.

Types of Dart Collections