List.shuffle() in Dart?

Question

I'm looking every where on the web (dart website, stackoverflow, forums, etc), and I can't find my answer.

So there is my problem: I need to write a function, that print a random sort of a list, witch is provided as an argument. : In dart as well.

I try with maps, with Sets, with list ... I try the method with assert, with sort, I look at random method with Math on dart librabry ... nothing can do what I wana do.

Can some one help me with this?

Here some draft:

var element03 = query('#exercice03');
  var uneliste03 = {'01':'Jean', '02':'Maximilien', '03':'Brigitte', '04':'Sonia', '05':'Jean-Pierre', '06':'Sandra'};
  var alluneliste03 = new Map.from(uneliste03);
  assert(uneliste03 != alluneliste03);
  print(alluneliste03);

  var ingredients = new Set();
  ingredients.addAll(['Jean', 'Maximilien', 'Brigitte', 'Sonia', 'Jean-Pierre', 'Sandra']);
  var alluneliste03 = new Map.from(ingredients);
  assert(ingredients != alluneliste03);
  //assert(ingredients.length == 4);

  print(ingredients);

  var fruits = <String>['bananas', 'apples', 'oranges'];
  fruits.sort();
  print(fruits);

Solution 1

Here is a basic shuffle function. Note that the resulting shuffle is not cryptographically strong. It uses Dart's Random class, which produces pseudorandom data not suitable for cryptographic use.

import 'dart:math';

List shuffle(List items) {
  var random = new Random();

  // Go through all elements.
  for (var i = items.length - 1; i > 0; i--) {

    // Pick a pseudorandom number according to the list length
    var n = random.nextInt(i + 1);

    var temp = items[i];
    items[i] = items[n];
    items[n] = temp;
  }

  return items;
}

main() {
  var items = ['foo', 'bar', 'baz', 'qux'];

  print(shuffle(items));
}

Solution 2

There is a shuffle method in the List class. The methods shuffles the list in place. You can call it without an argument or provide a random number generator instance:

var list = ['a', 'b', 'c', 'd'];

list.shuffle();

print('$list');

---

The collection package comes with a shuffle function/extension that also supports specifying a sub range to shuffle:

void shuffle (
  List list,
  [int start = 0,
  int end]
)

Comments

[Alexandre Ardhuin]

There's a difference between your code and the modern algorithm of Knuth suffle. Is it wanted ? ( random.nextInt(items.length) vs. random.nextInt(j + 1) )

[Kai Sellgren]

No, it wasn't intentional :). Fixed.

[Christophe Herreman]

Actually shouldn't it be: random.nextInt(i+1) according to the modern algorithm?

[Deleplace]

Indeed n = random.nextInt(items.length) is really flawed. See en.wikipedia.org/wiki/… for details.

[Oliver Dixon]

It's a shame it doesn't return the list for streams etc.

[Kai Sellgren]

@LechMigdal I updated my original answer so it's up to date now.

[Vinoth Vino]

items..shuffle(); worked for me. It returns a list of objects

[Randal Schwartz]

And of course, you should be using List.shuffle these days, not this handrolled code.