code: public final <V> Flux<T> distinctUntilChanged(Function<? super T, ? extends V> keySelector) {
  		return distinctUntilChanged(keySelector, equalPredicate());
  	}
docs: Filter out subsequent repetitions of an element (that is, if they arrive right after
  one another), as compared by a key extracted through the user provided {@link Function}
  using equality.
  
  <p>
  <img class="marble" src="doc-files/marbles/distinctUntilChangedWithKey.svg" alt="">
  
  @reactor.discard This operator discards elements that are considered as "already seen".
  The keys themselves are not discarded.
  
  @param keySelector function to compute comparison key for each element
  @param <V> the type of the key extracted from each value in this sequence
  
  @return a filtering {@link Flux} with only one occurrence in a row of each element of
  the same key (yet element keys can repeat in the overall sequence)