Reduce List<T> using BiFunction<T, T, Mono<T>>

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I have List<T>, I need to reduce it using BiFunction<R, T, Mono<R>> aggregator.

So I need to chain those monos (Mono<R>) How this can be done using project reactor?

UPDATE: For example, I have a list with item1, item2 etc... I have a function Mono<R> reduce(T item, R acc)

I need something like this: reduce(item1, startAcc).flatMap(acc -> reduce(item2, acc)).flatMap(acc -> reduce(item3, acc)) etc.

I can implement this using recursion, but I get StackOverflowError if the list is long enough

project-reactor reactive-programming mono java
1 Answers

You should simply use the reduce method available on Flux. Sample code below:

public void reduceTest() {

    List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
    Flux<Integer> numberFlux = Flux.fromIterable(numbers);

    Double initial = 2.5;
    BiFunction<Double, Integer, Double> multiply = (doubleNumber, numberInt) -> doubleNumber * numberInt;

    Mono<Double> floatResult = numberFlux.reduce(initial, multiply);        
    floatResult.subscribe(System.out::println);

}

Please refer the Java Docs at https://projectreactor.io/docs/core/release/api/index.html?reactor/core/publisher/Mono.html

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