JavaFX 8 allows to fluently filter and sort observable lists by dynamically mapping index positions, using the FilteredList and SortedList classes.

While this is indeed very useful, unfortunately there is one brick missing in the complete vision of dynamic list transforms: Type and content mapping. For example, a data model might provide an observable list of customers, while the user interface shall provide a list which contains that customer's last name only. And certainly, the list shall be "live", i. e. when the customer list is changed, the list of last names shall change in the same way. In fact, some controls are able to provide help with that (like TableView), while other controls might not (like TreeView), or even worse, the derived list might be needed for further processing steps before getting rendered.

A proposed solution would be to add a new class MappedList<T> (a prototype of this can be found attached to this RFE), and returning that one as the result of a new fluent operation ObserverableList<F>.map(Function<F, E> mapper). This class does nothing but simply applies the provided mapper function whenever ObservableList<E>.get(int) is called. So the mapping happens "on the fly", in a comparable way like Stream.map(Function) and Optional.map(Function) are working like. As the mapped value is not stored, hardly no additional memory is required. As typically the mapping functions are provided as method handles of element's methods (like Customer::getLastName) the execution speed of the live mapping is negligible.

It would be a great help for any complex application to offload this mapping work to the JavaFX framework.