src/main/java/io/reactivex/Single.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <U, R> Single<R> zipWith(SingleSource<U> other, BiFunction<? super T, ? super U, ? extends R> zipper) {
        return zip(this, other, zipper);
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <U, R> Single<R> zipWith(SingleSource<U> other, BiFunction<? super T, ? super U, ? extends R> zipper) {
        return zip(this, other, zipper);
    }
Returns a Single that emits the result of applying a specified function to the pair of items emitted by
the source Single and another specified Single.
<p>
<img width="640" height="380" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Single.zip.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code zipWith} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param <U>
the type of items emitted by the {@code other} Single
@param <R>
the type of items emitted by the resulting Single
@param other
the other SingleSource
@param zipper
a function that combines the pairs of items from the two SingleSources to generate the items to
be emitted by the resulting Single
@return a Single that pairs up values from the source Single and the {@code other} SingleSource
and emits the results of {@code zipFunction} applied to these pairs
@see <a href="http://reactivex.io/documentation/operators/zip.html">ReactiveX operators documentation: Zip</a>