Thank you all for your kindly responses, in meantime and after a short struggle with my miss-understandings I finally solved the problem and the exercise is working well! I learned a lot from this "AppEventCount" exercise in the data collections book. Thank you Claude31, the first of the two last links seems to me a good reference or at least there is there links to more actual solutions. I wish to all a nice day and thanks again. Ernesto.

Thank you for your replay, I think that is a misunderstanding here, I give the functions above only as some examples, my real question was: where in some Apple site I can observe the use of the functions / methods that we found in the documentation of Apple. After studying from the book "Developing in Swift - Fundamentals" I started the "Developing in Swift -Data collections", I feel that there is some issues that I don't understand and may be I'll receive more information about if I can read more from examples of code from Apple. Because I do not found some site like that I was thinking that some one of this community can help with some link to some site of Apple. Anyway thank you all. Ernesto.