Putting filter in message mapping

I am trying to put a filter for company codes such that if a type of company code comes in the file from source, it will filter out and send it to target system. I have set of company codes and values that I want to pass but want to filter out some company codes with certain values only. How can I achieve that? One possible way I can think of is If/then/Else logic with fixed values mapping.

Is there a blog or step by step guide? Can anyone help how I can do this in message mapping?

Thanks for your help.