Hi Lisa1993,

Thanks again for your help, and sorry if this post was inappropriate

We get a lot of posts from people with thinly veiled requests of "do my (home)work for me for free". To set yourself apart from those, I'd recommend you follow the advice in these links: How do I post a question effectively?, Short, Self Contained, Correct Example, and Basic debugging checklist, and what I think is most important, show your own efforts! If you've solved your own problem, you could post an update showing how you solved it, so that other wisdom seekers may learn from your question and its resolution. I think most monks are very happy to help those who want to learn!

Regards,
-- Hauke D

Hi haukex,

Thank you very much for the links: they are incredibly helpful, and I will be sure to follow the guidelines when I post in future. I would never want to come across as some kind of freeloader! I contribute to quite a lot of specialised forums in other subject areas, and I know from experience that it is incredibly frustrating when someone comes along and appears to be taking advantage of the knowledge of the forum members.

I will now update my original post with an edit that reflects the working code. Thanks again for your kindness and advice.

Lisa