Could I put two same type collection into one DataGrid and split them into two group?

[Flithor]

What I want to do:

AvaloniaList<MyItem> One = [/*someItems*/];
AvaloniaList<MyItem> Two = [/*someItems*/];
SomeCollectionContainer myContainer = [One, Two];
DataGrid_Display.ItemsSource = myContainer;

One.Add(SomeItem);
One.Remove(SomeItem);
myContainer[1] = NewTwo;

DataGrid will show One and Two as grouping view one by one, and display MyItem items in them.
And update with notifying, and can replace collection.

Current progress of research that looks I need implement IDataGridCollectionView from beginning.

Is there any way can make it easier?

[thevortexcloud]

You can use the built in grouping functionality. There is some samples here:
https://github.com/AvaloniaUI/Avalonia.Controls.DataGrid/blob/master/src/DataGridSample/DataGridPage.axaml.cs

[Flithor]

Uh? I need keep the inner collections behavior, and grouping by exists collection not property.

[Flithor]

Well, I'm done.
To those who come later:

public class MyVM: ReactiveObject
{
    private readonly ObservableCollectionExtended<MyItem> one = [];
    private ObservableCollectionExtended<MyItem> two = [];
    private ObservableCollectionExtended<MyItem> Two
    {
        get => two;
        set => this.RaiseAndSetIfChanged(ref two, value);
    }
    private ReadOnlyObservableCollection<MyItem>? combineCollection;

    // ItemsSource Binding property
    public DataGridCollectionView ViewSource { get; }
        
    public MyVM()
    {
        var streamOne = one.ToObservableChangeSet();
        // monitor property Two and convert new value into new ChangeSet source
        var streamTwo = this.WhenAnyValue(vm => vm.Two)
            .Select(source => source.AsObservableChangeSet())
            .Switch(); // auto switch new source
    
        // Combine two source and bind to output property
        streamOne.Or(streamTwo) // add more source here with Or predicate
            .Bind(out combineCollection, 0)
            .Subscribe();
        
        ViewSource = new DataGridCollectionView(combineCollection);
        // custom GroupDescription
        ViewSource.GroupDescriptions.Add(new GroupByCollectionDescriptions(
            ("In One", item => one.Contains((MyItem)item)),
            ("In Two", item => two.Contains((MyItem)item))
        ));
    }

    private class GroupByCollectionDescriptions(params (object groupTitle, Func<object, bool>)[] checkDelegate) : DataGridGroupDescription
    {
        public override object GroupKeyFromItem(object item, int level, CultureInfo culture)
        {
            foreach (var (groupTitle, checkFunc) in checkDelegate)
            {
                if (checkFunc(item)) return groupTitle;
            }
            return "Abnormal: Out of collection";
        }
    }
}

// Dummy
public class MyItem : ReactiveObject;

[Flithor]

Of course, the performance of it is extremely poorly.
(Too many list Contains checks, but this is unavoidable.)

I'm trying TreeDataGrid solution.