Converter with collection
public object Convert(object value, Type targetType, object parameter,   System.Globalization.CultureInfo culture)
    {
        var collection = (ObservableCollection<OrderEntry>)value;
        var viewSource = new CollectionViewSource()
        {
            Source = collection,
        };
        viewSource.Filter += new FilterEventHandler(FilterInSealedOrderEntries);
        return viewSource.View;
    }

    private static void FilterInSealedOrderEntries(object sender, FilterEventArgs e)
    {
        var orderEntry = e.Item as OrderEntry;
        e.Accepted = orderEntry != null && orderEntry.Sealed;
    }