Filter only select duplicates

I have a list of cases for clients. They are either open or closed. I need to filter the list, so I have only one line per client left. If all cases are closed, I don't care, which line, but if there is at least one open case, I need to have an open case after filtering for duplicates.

I need to do this daily for tracking, so it should be easy to apply. And I get the source file from an external system. Any ideas on how to solve this?

Thanks for your help.