rxgroups/src/main/java/com/airbnb/rxgroups/ObservableGroup.java
public <T> void resubscribe(TaggedObserver<? super T> observer, String observableTag) {
    final Observable<T> observable = observable(observer, observableTag);
    if (observable != null) {
      observable.subscribe(observer);
    }
  }
public <T> void resubscribe(TaggedObserver<? super T> observer, String observableTag) {
    final Observable<T> observable = observable(observer, observableTag);
    if (observable != null) {
      observable.subscribe(observer);
    }
  }
Resubscribes the {@link TaggedObserver} to the observable identified by {@code observableTag}.