etl

public class Etl {


    public Map<String, Integer> transform(Map<Integer, List<String>> old){

        Map<Stream<String>, Integer> collect = old.entrySet() //Map.Entry<Integer, List<String>>
                .stream() //Stream<Map.Entry<Integer, List<String>>>
                .collect(Collectors
                        .toMap((Map.Entry<Integer, List<String>> entry) -> entry.getValue() //List<String>
                                        .stream() //Stream<List<String>>
                                        .map(Function.<String>identity()),
                                (Map.Entry<Integer, List<String>> entry2) -> entry2.getKey()));


        




        return null;
    }
}