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.

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.