public TextSpinner<T> setTextGroupMapper(final Func1<T, String> textGroupMapper) {
        this.textGroupMapper = textGroupMapper;
        return this;
    }
if spinner is be represented as a textview, set whether to group entries in dialog -> in this case, provide a mapper for each element to its group
main/src/main/java/cgeo/geocaching/ui/TextSpinner.java