Question

How would one implement LINQ to extract the Guid’s from one collection of objects of type A such that they can exclude these Guids from another collection of objects of type B. Object A and Object B both have a Guid field called ‘ID.”

I have the following:

1. ObservableCollection<Component> component Component has a
   field called ID of type Guid
2. ObservableCollection<ComponentInformation> ComponentInformationCollection ComponentInformation
   has a field called ID of type Guid

My implementation:

component =>
{
    if (component != null)
    {
        var cancelledComponents = new List<ComponentInformation>();
        foreach (Component comp in component)
        {
            cancelledComponents.Add(new ComponentInformation() { ID = comp.ID });
        }
        this.ComponentInformationCollection.Remove(cancelledComponents);
    }
});

I believe there is a more elegant solution which I’ve been working at to solve but the issue I keep running into is creating a ‘new ComponentInformation’ such that the types do not give me an error.

====== FINAL SOLUTION =======

var cancelledComponentIDs = new HashSet<Guid>(component.Select(x => x.ID));
this.ComponentInformationCollection.Remove(
     this.ComponentInformationCollection.Where(x => cancelledComponentIDs.Contains(x.ID)).ToList());

Thank you to:
Jason – I used this as a template for my final solution (listed below).
Servy – While I could have used a comparer, I think for this particular scenario a comparer was not neccessary because of its one-time-use type of situation.

ComponentInformationCollection is a Silverlight DependencyProperty that will trigger a INotifyChangedEvent (MVVM pattern) when altered, so the solution above worked best for my situation.

Answer 1

I would do this:

var ids = new HashSet<Guid>(
              component.Select(x => x.ID)
          );
var keepers = ComponentInformationCollection.Where(x => !ids.Contains(x.ID));