// build a song to represent a group
// the GetChildDataItems method returns all songs that belong
// to this node, and the LINQ statement below calculates the total
// size, length, and average rating for the album/artist.
Song BuildGroupDataItem(GroupRow gr)
{
var gs = gr.GetDataItems().OfType <Song>();
return(new Song()
{
Name = gr.Group.Name.ToString(),
Size = (long)gs.Sum(s => s.Size),
Duration = (long)gs.Sum(s => s.Duration),
Rating = (int)(gs.Average(s => s.Rating) + 0.5)
});
}