List<Category> of physical element using LinQ and Categories list in VG

[Shai.Nguyen]

It seems an old problem, but I find in forum for long time and didn't find solution.

Question 1:

My Idea is get a List<Category> of physical element. Here is my code

ICollection<Element> allElelements = new FilteredElementCollector(doc, doc.ActiveView.Id).WhereElementIsNotElementType()
                    .Where(x => (x.Category != null) && x.GetTypeId() != null)
                    .Where(x => x.IsPhysicalElement())
                    .ToList();
List<Category> catList = allElelements
                .Select(x => x.Category)
                .Distinct()
                .ToList();

But maybe Distinct is not working here so that the list has duplicate categories.

How can I fix my code?

Question 2:

I want to get all category list of VG overrides in tab "Model Categories"

I use Category.CategoryType = CategoryType.Model but it contains some Categories that i don't want to.

Thank you in advanced. Your solution is appriciated. 

[Shai.Nguyen]

Question 3:
How Can I sort a List<Category>?

I found a topic that: https://forums.autodesk.com/t5/revit-api-forum/find-all-categories-with-instances/m-p/7246344/highli...

It's seem be like what I want. but I don't know what class "CategoryNameComparer" is..

[RPTHOMAS108 · Accepted solution]

The Category class has a property CategoryType which returns an enum value such as Model, so you can filter by this. Before this was invented I used to filter by HasMaterialQuantities but I recently discovered in the UI some Model categories don't have a material quantity. Would have been nice to know the volume of a stair at one point.

This is more of a general .Net question than RevitAPI.

List(T).Distinct() will only work if the class implements IEquatable(of T), not sure if this has been done for the Category class. If it hasn't then you need to use the .Distinct overload that takes a class that implements IEqualityComparer(Of T).

Similarly to sort items the Category class would have to implement IComparable(Of T), it may exist however sorts by something other than name e.g. ID (not sure). Again you can use an overload for .Sort that takes a class that implements IComparer(of T).

This can be as simple as below since string has a default comparer:

public class Example
{
	public void SortCategories()
	{
		List<Category> C = new List<Category>();
		//Sort
		C.Sort(new MyCategoryComparerByName());
		//Unique
		C = C.Distinct(new MyCategoryEqualityComparer()).ToList;
	}
	private class MyCategoryComparerByName : IComparer<Category>
	{
		public int Compare(Category x, Category y)
		{
			return string.Compare(x.Name, y.Name);
		}
	}
	private class MyCategoryEqualityComparer : IEqualityComparer<Category>
	{

		public bool Equals(Category x, Category y)
		{
			return x.Id == y.Id;
		}

		public int GetHashCode(Category obj)
		{
			return obj.Id.IntegerValue;
		}
	}
}

[RPTHOMAS108]

As a less verbose alternative to the about you can use Lambda expressions with the LINQ extensions but that may be harder to understand if you've first not considered how the basic interfaces mentioned above work.

[Shai.Nguyen]

thank you Thomas. Your solution is what I've been looking for these day. It seems that there are a lot of thing I have to learn. 🙂