At work, I had a spreadsheet. Technical people, coders even, had a hard time finding the solution: convert to CSV, cut -f, awk print, in order to tack a hostname onto a column with relative HTTP paths. (No error checking required.)
If you were using Excel, you code have just written a VBA macro to do it, or created another column with formula =CONCATENATE("http://domain/",A1) if that's what you mean