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);

What do you mean "random sort"? Are you trying to put the elements in random order? — beatgammit, Nov 25 '12 at 18:39
In that case, take a look at [shuffling algorithms](http://www.codinghorror.com/blog/2007/12/shuffling.html). I don't have time to come up with a full solution, but hopefully this helps. Also check out this [SO question](http://stackoverflow.com/questions/375351/most-efficient-way-to-randomly-sort-shuffle-a-list-of-integers-in-c-sharp) — beatgammit, Nov 25 '12 at 18:44
Thx I'll look at this, if any one can come with a solution I will appreciate as well ! — Peter, Nov 25 '12 at 18:47
Here's the bug requesting this feature, please star it to vote for it: http://code.google.com/p/dart/issues/detail?id=6788 — Seth Ladd, Nov 26 '12 at 06:38
There is a List.shuffle method implemented in the List class since some months — Fox32, May 28 '14 at 08:05

Fox32 · Answer 1 · 2021-08-27T07:34:20.937

167

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]
)

edited Aug 27 '21 at 07:34

answered May 28 '14 at 08:04

Fox32

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It's a shame it doesn't return the list for streams etc. – Oliver Dixon Jun 13 '19 at 09:22
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@LechMigdal I updated my original answer so it's up to date now. – Kai Sellgren Jun 16 '19 at 11:29
17

`items..shuffle();` worked for me. It returns a list of objects – Vinoth Vino Jul 30 '20 at 17:26

score 38 · Accepted Answer · edited Jun 19 '19 at 01:19

38

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));
}

edited Jun 19 '19 at 01:19

Bhargav Rao

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answered Nov 25 '12 at 22:28

Kai Sellgren

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There's a difference between your code and the [modern algorithm of Knuth suffle](http://en.wikipedia.org/wiki/Knuth_shuffle#The_modern_algorithm). Is it wanted ? ( `random.nextInt(items.length)` vs. `random.nextInt(j + 1)` ) – Alexandre Ardhuin Nov 26 '12 at 07:19
No, it wasn't intentional :). Fixed. – Kai Sellgren Nov 27 '12 at 08:39
1

Actually shouldn't it be: random.nextInt(i+1) according to the modern algorithm? – Christophe Herreman Nov 27 '12 at 11:11
1

Indeed `n = random.nextInt(items.length)` is really flawed. See http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle#Potential_sources_of_bias for details. – Deleplace Sep 04 '14 at 11:34
3

And of course, you should be using List.shuffle these days, not this handrolled code. – Randal Schwartz Jan 11 '21 at 18:23

score 5 · Answer 3 · answered Dec 29 '22 at 20:07

5

You can use shuffle() with 2 dots like Vinoth Vino said.

List cities = ["Ankara","London","Paris"];

List mixed = cities..shuffle();

print(mixed);

// [London, Paris, Ankara]

answered Dec 29 '22 at 20:07

Kasım Onuk

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List.shuffle() in Dart?

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