How to create a new filtered collection when the source collection's property changed?

[Snailya]

I'm writing a canExecute observable using reactive ui and dynamic data.
In my view, I have a ListBox with checkable item. I want to observe on this checkbox and set the canExecute to true is any of the item is checked. So i convert the itemssource for the listbox named Items to IChangeSet by ToObservableChangeSet(). I've noticed that it will notified only by calling Items.ToObservableChangeSet().WhenPropertyChanged(x=>x.IsChecked). But I don't know how to create a new filtered output collection whenever it notifies.

[JakenVeina]

So, you need an IObservable<bool> that is true when there is at least one item in the set that is selected?

Pull the DynamicData.Aggregations namespace and do...

items
    .FilterOnObservable(static item => item.WhenPropertyChanged(x => x.IsChecked))
    .IsNotEmpty();

[Snailya]

Thanks