List Operators #

Introduction #

The package list_operators uses Dart extensions to provide additional operators for objects of type List<num> and List<T extends Comparable>.

Usage #

To use this package include list_operatos as a dependency in your pubspec.yaml file. The program below demonstrates how to use some of the operators and methods defined by the library list_operators.

Note: The + operator (concatenates two lists) is already defined by Dart's abstract class List and cannot be overridden by an extension on List. To add two numerical lists element by element use the method: List<num> plus(List<num> other).

import 'package:list_operators/list_operators.dart';

void main() {
  final a = [1, 2, 3];
  final b = [11, 12, 13];

  /// Use with List<num>
  print('Absolute value:');
  print((a - b).abs());

  print('\nAddition:');
  print(a.plus(b));

  print('\nSubtraction:');
  print(b - a);

  print('\nInner product:');
  print(a.innerProduct(b));

  print('\nMultiplication:');
  print(a * 10);

  print('\nPower');
  print(a.pow(2));

  print('\nb.distanceFromOrigin()');
  print(b.distanceFromOrigin);

  print('\nb.distance(a)');
  print(b.distance(a));


  /// Use with List<T extends Comparable>
  print('\na < b:');
  print(a < b);

  print('\na <= b:');
  print(a <= b);

  print('\na > b:');
  print(a > b);

  print('\nb >= b:');
  print(b >= b);

  final s1 = ['a1', 'a2'];
  final s2 = ['b1', 'b2'];

  print('\ns1 <= s2');
  print(s1 < s2);

  /// Provided by Dart
  print('\nConcatenation:');
  print(a + b);

  /// Exporting numerical lists to a `String` object.
  print('\nExporting lists to String:');
  print(a.export(
    label: 'Sample label',
    delimiter: ', ',
    precision: 4,
  ));

  print('\nExporting an object of type List<List<num>> to String:');
  print('Each inner list is exported as a row.');
  print([
    [1, 2, 3],
    [101, 102, 103]
  ].export(label: 'Sample label', precision: 6));

  print('\nExporting an object of type List<List<num>> to String.');
  print('Inner lists are exported as columns.');
  print([
    [1, 2, 3],
    [101, 102, 103]
  ].export(
    label: 'Sample label',
    precision: 6,
    flip: true,
  ));

  // Creating an unmodifiable list view (recursively)
  print('\nCreating an unmodifiable list of an object of type List<List<T>>:');
  final list = [
    ['one'],
    ['two'],
  ];

  // Extension works for objects of type List<T> and List<List<T>>
  final listView = list.unmodifiable();

  // Prints: UnmodifiableListView<UnmodifiableListView<String>>
  print(listView.runtimeType);
}

dan@nano:~/list_operators$ dart example/bin/example.dart
Absolute value:
[10, 10, 10]

Addition:
[12, 14, 16]

Subtraction:
[10, 10, 10]

Scalar product:
74

Multiplication:
[10, 20, 30]

Power
[1, 4, 9]

b.distanceFromOrigin()
20.83266665599966

b.distance(a)
17.320508075688775

a < b:
true

a <= b:
true

a > b:
false

b >= b:
true

s1 <= s2
true

Concatenation:
[1, 2, 3, 11, 12, 13]

Exporting lists to String:
Sample label
1.000,
2.000,
3.000,


Exporting an object of type List<List<num>> to String:
Each inner list is exported as a row.
Sample label
1.00000 2.00000 3.00000
101.000 102.000 103.000


Exporting an object of type List<List<num>> to String.
Inner lists are exported as columns.
Sample label
1.00000 101.000
2.00000 102.000
3.00000 103.000


Creating an unmodifiable list view of an object of type List<List<T>>:
[[one], [two]]   runtimeType: UnmodifiableListView<UnmodifiableListView<String>>

Limitations #

In its current version, Dart does not support function (and implicitly operator) overloading. For this reason some numerical operations defined by list_operators are not symmetrical, even though intuitively they should be:

• The expression [1, 2, 3] * 10 is defined and the result is [10, 20, 30].
• The expression 10 * [1, 2, 3] is not defined since the * operator defined for objects of type int expects a second operand of type num.

Examples #

The program shown above is included in the folder example.

Features and bugs #

Please file feature requests and bugs at the issue tracker.