func filterValues(search: String, author: String = "") {
   if search.isEmpty && author.isEmpty {
      filteredItems = userData.sorted(by: { $0.title < $1.title })
   } else {
      let list = userData.filter( { item in
         var valid = true
         if !author.isEmpty && author != item.author {
            valid = false
         }
         if valid && !search.isEmpty && !item.title.localizedStandardContains(search) {
            valid = false
         }
         return valid
      })
      filteredItems = list.sorted(by: { $0.title < $1.title })
   }
}