How to Handle Variable Input List Length/Nesting in Custom Nodes (Python)

Bo_Steadman · February 16, 2016, 5:59pm

Has anyone found a good method for handling various input types in a custom node? I’m trying to find a python or OOTB solution that allows me to take a variable input (flat list, nested list, single item, etc) and to turn it into the same type of list structure. I tried using flatten and list.join, but that doesn’t work for single items that are not part of a list yet. List.create causes problems for already nested lists. Thoughts?

Steven · February 16, 2016, 6:57pm

What are you trying to do? Just get two of any type of list to look the same? Lists are normally organized on a script bases and have a reason for being done the way it was.

You can defiantly use OOTB nodes to organize a list any way you want but it depends on what you want the list to do.

Bo_Steadman · February 16, 2016, 7:14pm

I essentially just need a flat list. The input could be a single item (taken from “Select Model Element” node) a nested list, or a flat list. The goal is to make the node more user-friendly so that one doesn’t have to know the exact nesting required.

Steven · February 16, 2016, 7:27pm

Have you tried using list flatten?

Dimitar_Venkov · February 16, 2016, 8:23pm

Have you tried defining your inputs? That way you’ll enable lacing and as long as there’s a logical way, the Dynamo VM will map the inputs to the function correctly.

This will first make sure to check that the input is for example indeed a point type. Secondly it’ll automatically convert it to a single object, a list or a matrix depending on your definition.

This also works for python scripts, but from my experience it has a negative effect on performance when dealing with large data sets.

Konrad_K_Sobon · February 16, 2016, 8:59pm

Bo, can you post this question on Stack Overflow like I have asked before and I will post some Python examples for your use. Please reply to this post with a link to SO question.

Organon · February 16, 2016, 10:38pm

I’m trying to do the same, but something tells me this i s not the right way:

IsList

Gif01

Dimitar_Venkov · February 16, 2016, 11:43pm

Here’s a basic example with a python node. The below is two identical scripts, the first one has a defined input as a single object, the second one is left undefined. This way you can skip doing any checks in the python node but as I said earlier, performance will suffer on large data sets(compared to zero touch or built-in nodes) because the python code will have to be re-evaluated for each item:

Bo_Steadman · February 19, 2016, 4:42pm

Topic posted here:

Bo_Steadman · February 19, 2016, 6:48pm

Dimitar, after reading through your response, I saw that you actually had an answer for the question. I thought that the input nodes only allowed one to structure something of a certain type (point, line, integer) which is why I thought your response would not work for me, but after reading through your response and also Colin McCrone’s post on the blog (http://dynamobim.org/what-does-var-mean/) I see that I can use var[] as the input, which will automatically flatten or create a list to match a flat list structure for any input type. Works great, thanks!

Konrad_K_Sobon · February 20, 2016, 7:08pm

Bo I answered your question @ Stack Overflow. Thanks for posting.

Organon · February 23, 2016, 11:35am

Thanks to everyone.

Konrad_K_Sobon · February 23, 2016, 2:30pm

Bo, would you be kind enough and approve the answer on SO if that is indeed an answer that satisfies you. Thank you,

teocomi · August 17, 2016, 2:02pm

Hello, this thread is very helpful. But can anyone suggest how to do the same in C#?
If I use object it will just recuse the input at the item level, if I use List<object> instead it will ignore nested lists.

What is the equivalent of var[]…[] in C#?

Konrad_K_Sobon · August 17, 2016, 5:27pm

I think that setting the input to List<object> also enables nested lists. Then you would have to play with lacing to get it right. Care to post a sample code + dll of the issue?

teocomi · August 17, 2016, 5:52pm

Apparently the solution is to use: [ArbitraryDimensionArrayImport] object item

See:

github.com

DynamoDS/Dynamo/blob/master/src/Libraries/CoreNodes/List.cs#L342


var result = new ArrayList();
int len = list.Count;


if (offset <= 0)
    throw new ArgumentException("Must be greater than zero.", "offset");


for (int start = 0; start < len; start += offset)
{
    var row = new List<object>();


    foreach (object item in ranges)
    {
        List<int> subrange;


        if (item is ICollection)
            subrange = ((IList)item).Cast<int>().Select(Convert.ToInt32).ToList();
        else
            subrange = new List<int> { Convert.ToInt32(item) };


        row.AddRange(
            subrange.Where(idx => start + idx < len).Select(idx => list[start + idx]));

Thanks to:

Konrad_K_Sobon · August 17, 2016, 6:17pm

Interesting. Thanks for sharing I didn’t know that one either. It would really make a difference if they posted that stuff somewhere in one place.

Konrad_K_Sobon · August 17, 2016, 9:36pm

@teocomi since there isn’t really a good resource for Zero Touch I have started to collect these little nuances into a blog post. I added your findings to it as well. http://archi-lab.net/tips-tricks-for-zerotouch-libraries-in-dynamo/

Organon · September 6, 2016, 11:51pm

The Konrad’s function using lists comprehension:

elements = IN[0]

ProcessLists = lambda function, lists: [ProcessLists(function, item) if isinstance(item, list) else function(item) for item in lists]

sum = lambda x: x + 1

if isinstance(elements, list):
    out = ProcessLists(sum, elements)
else:
    out = sum(elements)

OUT = out

ali.safiaddine · January 9, 2017, 8:39am

Hi guys ,
Thank you this is very helpful

but trying to change a python code to get variable input but actually with my little experience in python I did not succeed

the python script is provided by @Einar_Raknes by it only take one element as an input

Can anyone please solve this for me just to get more familiar with python scripts

Thank you

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How to Handle Variable Input List Length/Nesting in Custom Nodes (Python)

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