List.Shuffle shuffles nested lists incorrectly

[dimven]

Dynamo version

ever since 0.82:
http://dynamobim.org/forums/topic/random-list-of-lists/

Operating system

Windows 7

What did you do?

Ran some nested lists through a list-shuffle node

What did you expect to see?

Uniquely shuffled sub-lists

What did you see instead?

Identically shuffled lists:

This was reported previously and ignored:
DynamoDS/Dynamo#5977

[mjkkirschner]

@dimven yep yep! check out the implementation:
https://github.com/DynamoDS/Dynamo/blob/master/src/Libraries/CoreNodes/List.cs#L1161

the new random should be moved to the class level for the behavior you are expecting as it's set to a seed based on the clock. When called all at once we get the same random numbers.

@ke-yu what do you think?

[dimven]

Sounds good to me. Alternatively, we can follow this SO:
http://stackoverflow.com/questions/1785744/how-do-i-seed-a-random-class-to-avoid-getting-duplicate-random-values

and give it a unique seed every time. Seems to work well:

As a side note, since lists are the backbone of every Dynamo graph and you'd usually use at least a few list methods in every graph, has the team considered replacing some of those LINQ calls for the sake of memory efficiency?

[dimven]

Not sure if this is a good example, but the below seems to be about twice as fast:

static IList Shuffle2(IList list)
{
    var rng = new Random(Guid.NewGuid().GetHashCode());
    int[] vals = new int[list.Count];
    object[] data = new object[list.Count];
    for (int i = 0;
         i < list.Count;
         i++)
    {
    	vals[i] = rng.Next();
    	data[i] = list[i];
    }
    Array.Sort(vals, data);
    return (IList)data;
}

Unless I'm just pushing the burden off to somewhere else, like the marshaller...

[ke-yu]

@mjkkirschner we'll still get then same shuffled list each time open dynamo (will we?) if yes then using guid's hashcode or system tick count as see would be more "random"

[firas007noori]

Hi, I have no knowledge in Python, and I saw the solution for sublist shuffle here, and I used it, I thank you all, it worked for 2 days an suddenly the letter (a) in it turn into blue an it all stop working on one laptop, the other!! is still working normally with the letter (a) is not blue!!??
Any help is really appreciated, thanks in advance

[Amoursol]

This has now been fixed in Dynamo 2.10: https://dynamobim.org/dynamo-core-2-10-release/