RxJava中的n元笛卡尔积 [英] n-ary Cartesian product inRxJava

问题描述

现在我拥有一个Observable<Observable<Integer>，如何将其转移到包含n元笛卡尔积的Observable<int[]>中?

Now I hold an Observable<Observable<Integer>, how can I transfer it into Observable<int[]> that contains the n-ary Cartesian product?

例如:

Observable<Observable<Integer> ob = Observable.just(
  Observable.just(0,1),
  Observable.just(2,3),
  Observable.just(4,5)
  );
ob...... ->   (0,2,4), (0,3,4), (0,2,5), (0,3,5), (1,2,4), (1,3,4), (1,2,5), (1,3,5)

推荐答案

首先，您需要固定数量的输入Observable.其次，不需要阻塞，但是可能需要缓存，因为第二，第三等Observable需要多次使用.

First of all, you need a fixed number of input Observables. Second, there is no need for blocking but there is likely the need for caching because the 2nd, 3rd etc Observables need to be consumed multiple times.

import java.util.*;

import io.reactivex.Observable;

public class Cartesian {

    static Observable<int[]> cartesian(Observable<Observable<Integer>> sources) {
        return sources.toList().flatMapObservable(list -> cartesian(list));
    }

    static Observable<int[]> cartesian(List<Observable<Integer>> sources) {
        if (sources.size() == 0) {
            return Observable.<int[]>empty();
        }
        Observable<int[]> main = sources.get(0).map(v -> new int[] { v });

        for (int i = 1; i < sources.size(); i++) {
            int j = i;
            Observable<Integer> o = sources.get(i).cache();
            main = main.flatMap(v -> {
                return o.map(w -> {
                    int[] arr = Arrays.copyOf(v, j + 1);
                    arr[j] = w;
                    return arr;
                });
            });
        }

        return main;
    }

    public static void main(String[] args) {
        cartesian(Observable.just(
            Observable.just(0, 1), 
            Observable.just(2, 3), 
            Observable.just(4, 5)
        ))
        .subscribe(v -> System.out.println(Arrays.toString(v)));
    }
}

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