public final <U> ParallelFlux<U> composeGroup(Function<? super GroupedFlux<Integer, T>,
			? extends Publisher<? extends U>> composer) {
		if (getPrefetch() > -1) {
			return from(groups().flatMap(composer::apply),
				parallelism(), getPrefetch(),
				Queues.small());
		}
		else {
			return from(groups().flatMap(composer::apply), parallelism());
		}
	}
public final <U> ParallelFlux<U> composeGroup(Function<? super GroupedFlux<Integer, T>,
			? extends Publisher<? extends U>> composer) {
		if (getPrefetch() > -1) {
			return from(groups().flatMap(composer::apply),
				parallelism(), getPrefetch(),
				Queues.small());
		}
		else {
			return from(groups().flatMap(composer::apply), parallelism());
		}
	}
public final < U > ParallelFlux < U > composeGroup ( Function < ? super GroupedFlux < Integer , T > , ? extends Publisher < ? extends U > > composer ) { if ( getPrefetch ( ) > - 1 ) { return from ( groups ( ) . flatMap ( composer :: apply ) , parallelism ( ) , getPrefetch ( ) , Queues . small ( ) ) ; } else { return from ( groups ( ) . flatMap ( composer :: apply ) , parallelism ( ) ) ; } }
Allows composing operators off the 'rails', as individual {@link GroupedFlux} instances keyed by
the zero based rail's index. The transformed groups are {@link Flux#parallel parallelized} back
once the transformation has been applied.
<p>
Note that like in {@link #groups()}, requests and cancellation compose through, and
cancelling only one rail may result in undefined behavior.

@param composer the composition function to apply on each {@link GroupedFlux rail}
@param <U> the type of the resulting parallelized flux
@return a {@link ParallelFlux} of the composed groups
Allows composing operators off the rails as individual { @link GroupedFlux } instances keyed by the zero based rail s index . The transformed groups are { @link Flux#parallel parallelized } back once the transformation has been applied . <p > Note that like in { @link #groups () } requests and cancellation compose through and cancelling only one rail may result in undefined behavior .