Collection Operations in Dart

map()

Transforms each element and returns a new iterable:

var numbers = [1, 2, 3, 4, 5];
var doubled = numbers.map((n) => n * 2).toList();
print(doubled);  // [2, 4, 6, 8, 10]

var names = ['alice', 'bob', 'carol'];
var upper = names.map((n) => n.toUpperCase()).toList();
print(upper);  // [ALICE, BOB, CAROL]

where()

Filters elements that match a condition:

var nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
var evens = nums.where((n) => n % 2 == 0).toList();
print(evens);  // [2, 4, 6, 8, 10]

var scores = [45, 72, 88, 91, 55, 60];
var passed = scores.where((s) => s >= 60).toList();
print(passed);  // [72, 88, 91, 60]

reduce() & fold()

var nums = [1, 2, 3, 4, 5];

// reduce — combine elements (no initial value)
int sum = nums.reduce((a, b) => a + b);
print(sum);  // 15

int product = nums.reduce((a, b) => a * b);
print(product);  // 120

// fold — combine with an initial value
int sumFrom10 = nums.fold(10, (acc, n) => acc + n);
print(sumFrom10);  // 25

// fold works on empty lists; reduce throws on empty
var empty = <int>[];
int result = empty.fold(0, (acc, n) => acc + n);
print(result);  // 0

any() & every()

var ages = [15, 22, 30, 17, 45];

print(ages.any((a) => a >= 18));    // true (at least one adult)
print(ages.every((a) => a >= 18));  // false (not all adults)
print(ages.any((a) => a > 50));     // false

Full Example

void main() {
  var students = [
    {'name': 'Alice', 'score': 88},
    {'name': 'Bob', 'score': 54},
    {'name': 'Carol', 'score': 92},
    {'name': 'Dave', 'score': 61},
  ];

  var passed = students.where((s) => s['score'] as int >= 60).toList();
  var names = passed.map((s) => s['name']).toList();
  var avg = students.fold<int>(0, (sum, s) => sum + (s['score'] as int))
            / students.length;

  print('Passed: $names');
  print('Average: $${avg.toStringAsFixed(1)}');
  print('All passed: $${students.every((s) => (s['score'] as int) >= 60)}');
}

Passed: [Alice, Carol, Dave]
Average: 73.8
All passed: false

🧠 Quiz

Summary

Dart collections support functional operations: map() transforms, where() filters, reduce() combines, fold() combines with initial value, any() checks at least one match, every() checks all match. Chain them for powerful data processing pipelines.