question: public final < R > ParallelFlux < R > reduce ( Supplier < R > initialSupplier , BiFunction < R , T , R > reducer ) { Objects . requireNonNull ( initialSupplier , "initialSupplier" ) ; Objects . requireNonNull ( reducer , "reducer" ) ; return onAssembly ( new ParallelReduce < > ( this , initialSupplier , reducer ) ) ; }
target:  Reduces all values within a 'rail' to a single value (with a possibly different type) via a reducer function that is initialized on each rail from an initialSupplier value. <p> Note that the same mapper function may be called from multiple threads concurrently.