flutter-study-notebook/study_guide/Dart Collections.md

Dart Collections: A Comprehensive Guide

Dart provides several built-in collection types to help you manage and manipulate groups of objects. This guide covers the main collection types and their operations.

1. Lists

Lists are ordered, indexable collections of objects.

Example:

void main() {
  // Creating lists
  var numbers = [1, 2, 3, 4, 5];
  List<String> fruits = ['apple', 'banana', 'orange'];

  // Accessing elements
  print(numbers[0]); // 1
  print(fruits.last); // orange

  // Adding elements
  numbers.add(6);
  fruits.addAll(['grape', 'mango']);

  // Removing elements
  numbers.remove(3);
  fruits.removeAt(0);

  // Other operations
  print(numbers.length); // 5
  print(fruits.contains('banana')); // true
  
  // Iterating
  for (var fruit in fruits) {
    print(fruit);
  }

  // Functional operations
  var doubledNumbers = numbers.map((n) => n * 2).toList();
  var evenNumbers = numbers.where((n) => n.isEven).toList();
}

2. Sets

Sets are unordered collections of unique items.

Example:

void main() {
  // Creating sets
  var uniqueNumbers = {1, 2, 3, 4, 5};
  Set<String> uniqueFruits = {'apple', 'banana', 'orange'};

  // Adding elements
  uniqueNumbers.add(6);
  uniqueFruits.addAll(['grape', 'mango']);

  // Removing elements
  uniqueNumbers.remove(3);

  // Set operations
  var setA = {1, 2, 3, 4};
  var setB = {3, 4, 5, 6};
  print(setA.union(setB)); // {1, 2, 3, 4, 5, 6}
  print(setA.intersection(setB)); // {3, 4}
  print(setA.difference(setB)); // {1, 2}

  // Checking membership
  print(uniqueFruits.contains('banana')); // true

  // Iterating
  for (var number in uniqueNumbers) {
    print(number);
  }
}

3. Maps

Maps are collections of key-value pairs.

Example:

void main() {
  // Creating maps
  var ages = {'Alice': 30, 'Bob': 25, 'Charlie': 35};
  Map<String, int> scores = {'Math': 90, 'Science': 85, 'History': 95};

  // Accessing values
  print(ages['Alice']); // 30
  print(scores['Math']); // 90

  // Adding or updating entries
  ages['David'] = 28;
  scores.addAll({'Geography': 88, 'Literature': 92});

  // Removing entries
  ages.remove('Bob');

  // Checking keys and values
  print(ages.containsKey('Charlie')); // true
  print(scores.containsValue(100)); // false

  // Iterating
  ages.forEach((key, value) {
    print('$key is $value years old');
  });

  // Getting all keys or values
  print(scores.keys);
  print(scores.values);
}

4. Collection Methods and Operations

Dart provides many useful methods for working with collections.

Example:

void main() {
  var numbers = [1, 2, 3, 4, 5];

  // Functional methods
  var doubled = numbers.map((n) => n * 2);
  var evenNumbers = numbers.where((n) => n.isEven);
  var sum = numbers.reduce((a, b) => a + b);
  var product = numbers.fold(1, (a, b) => a * b);

  print(doubled); // (2, 4, 6, 8, 10)
  print(evenNumbers); // (2, 4)
  print(sum); // 15
  print(product); // 120

  // Sorting
  var fruits = ['banana', 'apple', 'orange'];
  fruits.sort();
  print(fruits); // [apple, banana, orange]

  // Reversing
  var reversedNumbers = numbers.reversed;
  print(reversedNumbers); // (5, 4, 3, 2, 1)

  // Shuffling
  numbers.shuffle();
  print(numbers); // Random order

  // Finding elements
  var firstEven = numbers.firstWhere((n) => n.isEven, orElse: () => -1);
  print(firstEven);
}

Conclusion

Dart's collection types provide powerful tools for managing groups of objects. Understanding how to effectively use Lists, Sets, and Maps, along with their associated methods and operations, is crucial for efficient Dart programming.