code: public final Observable<T> min(Comparator<? super T> comparator) {
          return OperatorMinMax.min(o, comparator);
      }
docs: Returns an Observable that emits the minimum item emitted by the source Observable, according to a
  specified comparator. If there is more than one such item, it returns the last-emitted one.
  <p>
  <img width="640" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/min.png" alt="">
  
  @param comparator
  the comparer used to compare elements
  @return an Observable that emits the minimum item emitted by the source Observable according to the
  specified comparator
  @throws IllegalArgumentException
  if the source is empty
  @see <a href="https://github.com/ReactiveX/RxJava/wiki/Mathematical-and-Aggregate-Operators#wiki-min">RxJava Wiki: min()</a>
  @see <a href="http://msdn.microsoft.com/en-us/library/hh229095.aspx">MSDN: Observable.Min</a>