C# GH Why error happens in my components?

Grasshopper
1

Hi everyone,
I’m new in scripting C# in GH.

I made component eliminating duplicate points.
It works well when I scripted in GH C# editor.
However, it occurs error when compiled by VisualStudio2017.

Does anyone know what is difference between GH C# Editor and VS2017?

Here attached is my .gh file contains both method, and here is my VS script.

elimduppoint.gh (12.6 KB)

Best,
Shimpei

protected override void SolveInstance(IGH_DataAccess DA)
_ {_
_ List pts = new List();_
_ List al = new List();_
_ DA.GetDataList(“pts”, pts);_

_ foreach (Point3d pt in pts)_
_ {_
_ if (!al.Contains(pt))_
_ {_
_ al.Add(pt);_
_ }_
_ }_

_ DA.SetData(“Unique”, al);_
_ }_

2

You need to use the generic version of List called List<T>. Type-safety is important.

protected override void SolveInstance(IGH_DataAccess DA)
{
  List<Point3d> points = new List<Point3d>();
  // Use parameter indices, not names to retrieve data if at all possible.
  if (!DA.GetDataList(0, points)) return; 

  // Always a good idea to initialize a list to an appropriate size.
  List<Point3d> filtered = new List<Point3d>(points.Count);

  // There are faster ways to find identical points, HashSet<Point3d> for one.
  // Also, you may want to add some tolerance checking rather than comparing
  // points exactly. 
  foreach (Point3d pt in points)
    if (!filtered.Contains(pt))
      filtered.Add(pt);

  DA.SetDataList(0, filtered);
}
3

If you’re getting warnings or errors, always post them. I cannot see your screen from here.

There are lots of differences, but only because the context within which the code executes is different. The language is the same.

4

Dear David,

Thank you for your answer!
Error is removed by scripting code you suggested.

I have one more question.
Componet by VS is faster than GH C# Editor?

Best,
Shimpei

5

It depends. Usually a little, but that is because the C# Scripts are compiled using a DEBUG flavour whereas you can choose to compile RELEASE on Visual Studio. Also there is less copying of data coming into the component, which can make a difference.

However given the code you posted, much bigger speed-ups can be gained by writing faster code. What you have there is a loop within a loop, meaning each additional point will take longer and longer to resolve. I think what you wrote is O(N^2). Using a better point searcher you can get it down to maybe O(log(N)).

6

Dear David,

I earned useful knowledge from you.
Thanks again!

I will focus on writing faster sode!

Best,
Shimpei

7

Specifically, the Contains() method on List<T> is an O(N) operation, because it compares the value against each and every element in the list, until it finds a match. This means that on a list twice as long it will take roughly twice as long to find a match, and exactly twice as long to determine there is no match.

The Contains() method on HashSet<T> on the other hand is O(1). It always takes the same amount of time, regardless of many items there already are in the set. The downside of HashSet<T> though is that it requires more memory and loses the order of points. So if you care about the ordering remaining intact, you will need to maintain both a list and a hashset.

A spatial subdivision of points such as for example an OcTree or a k-dTree will typically have O(log(N)) lookup, with the added benefit that you can specify a tolerance, so that points which are not exactly identical yet still very close together are still found as pairs. Sadly, the .NET framework does not have a standard collection type like this, but both RhinoCommon and Grasshopper do, to wit the Rhino.Geometry.RTree class and the Grasshopper.Kernel.Geometry.SpatialTrees.Node3d class.

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