Hi Dominique, I saw that you added an extension to Collection. I like the change, but I need to say two things: - please use just camel case in the names of the methods (no _) - actually, I would say that the fix would be better in the groupedBy: method. What do you say? Cheers, Doru -- www.tudorgirba.com www.tudorgirba.com/blog "When people care, great things can happen."