Question

I am trying to implement a simple sliding window function in RxJava2, but struggling to do what I want.

My goal is to take a stream of objects, i.e.

["a", "b", "c", "d", "e"]

and apply a sliding window which will return the elements adjacent to each element.

I.e resulting in:

["a", "b"]
["a", "b", "c"]
["b", "c", "d"]
["c", "d", "e"]
["d", "e"].

I.E.

a----------------b----------------c----------------d----------------e
↓                ↓                ↓                ↓                ↓
↓                ↓                ↓                ↓                ↓
↓                ↓                ↓                ↓                ↓
↓                ↓                ↓                ↓                ↓
["a", "b"]       ["a", "b", "c"]  ["b", "c", "d"]  ["c", "d", "e"]  ["d", "e"]

I can't seem to figure out how to make this happen. A Google Groups post seems like it is on the right track, but doesn't quite get the result I need: https://groups.google.com/forum/#!topic/rxjava/k-U5BijXinU

Any ideas?

Answer 1

根据您是否希望您的observable发出List<Item>或Observable<Item>，您可以使用buffer()或window()运算符。解决方案不是那么干净，但它非常简单：

Observable.fromArray("a", "b", "c", "d", "e")
        .startWith("")
        .buffer(3, 1)
        .map(strings -> {
            strings.remove("");
            return strings;
        })
        .filter(strings -> strings.size() > 1)

返回

["a", "b"]
["a", "b", "c"]
["b", "c", "d"]
["c", "d", "e"]
["d", "e"]

Answer 2

也许正如@jrook所说，这不适合标准窗口。数组大小本身并不足以知道您所在元素的哪一侧，所以我将其包含在一个简单的值类中。

这是我选择的解决方案。对于较大的流来说，它绝对不是一个好的解决方案，因为它阻止了首先读取整个可观察对象，这显然可能不适用于某些用例（在我的情况下，没关系）。

 public static <R> ObservableTransformer<R, AdjacentPairing<R>> pairWithAdjacents() {
    return upstream -> upstream
        .toList()
        .flatMapObservable(list -> {
          ArrayList<AdjacentPairing<R>> pairings = new ArrayList<>(list.size());
          for (int i = 0; i < list.size(); i++) {
            pairings.add(AdjacentPairing.from(
                i == 0 ? null : list.get(i - 1),
                list.get(i),
                i == list.size() -1 ? null : list.get(i + 1)));
          }
          return Observable.fromIterable(pairings);
        });
  }

  @AutoValue
  public static abstract class AdjacentPairing<T> {
    @Nullable
    public abstract T getPrevious();
    public abstract T getElement();
    @Nullable
    public abstract T getNext();

    public static <T> AdjacentPairing<T> from(@Nullable T previous, T element, @Nullable T next){
      return new AutoValue_RxUtils_AdjacentPairing<>(previous, element, next);
    }
  }

Implement a sliding window in RxJava2

2 个答案: