在Rx中实现滑动窗口的问题 [英] Trouble Implementing a Sliding Window in Rx
问题描述
我为响应式扩展创建了一个SlidingWindow
运算符,因为我想轻松监视滚动平均值之类的事情.作为一个简单的示例,我想订阅以听取鼠标事件,但是每次有一个事件我都想接收最后三个(而不是等待每三个事件接收最后三个).这就是为什么我发现Window重载似乎无法为我提供开箱即用的东西的原因.
I created a SlidingWindow
operator for reactive extensions because I want to easily monitor things like rolling averages, etc. As a simple example, I want to subscribe to hear mouse events, but each time there's an event I want to receive the last three (rather than waiting for every third event to receive the last three). That's why the Window overloads I found don't seem to give me what I need out of the box.
这是我想出的.考虑到它频繁的List操作,我担心它可能不是最有效的解决方案:
This is what I came up with. I fear that it might not be the most performant solution, given its frequent List operations:
public static IObservable<List<T>> SlidingWindow<T>(this IObservable<T> seq, int length)
{
var seed = new List<T>();
Func<List<T>, T, List<T>> accumulator = (list, arg2) =>
{
list.Add(arg2);
if (list.Count > length)
list.RemoveRange(0, (list.Count - length));
return list;
};
return seq.Scan(seed, accumulator)
.Where(list => list.Count == length);
}
可以这样称呼:
var rollingSequence = Observable.Range(1, 5).SlidingWindow().ToEnumerable();
但是,令我惊讶的是,没有收到预期的结果
However, to my great surprise, instead of receiving the expected results
1,2,3
2,3,4
3,4,5
我收到结果
2,3,4
3,4,5
3,4,5
任何见解将不胜感激!
推荐答案
试试看-我必须坐下来考虑一下它的相对性能,但这至少是 一样好,而且更易于阅读:
Try this instead - I'd have to sit and have a think about it's relative performance, but it's at least likely as good, and way easier to read:
public static IObservable<IList<T>> SlidingWindow<T>(
this IObservable<T> src,
int windowSize)
{
var feed = src.Publish().RefCount();
// (skip 0) + (skip 1) + (skip 2) + ... + (skip nth) => return as list
return Observable.Zip(
Enumerable.Range(0, windowSize)
.Select(skip => feed.Skip(skip))
.ToArray());
}
测试装备:
var source = Observable.Range(0, 10);
var query = source.SlidingWindow(3);
using(query.Subscribe(Console.WriteLine))
{
Console.ReadLine();
}
输出:
ListOf(0,1,2)
ListOf(1,2,3)
ListOf(2,3,4)
ListOf(3,4,5)
ListOf(4,5,6)
...
顺便说一句,自从不做一次就被烧死后,我就发现自己强迫自己.Publish().RefCount()
...我认为这不是严格要求的.
As an aside, I find myself compulsively .Publish().RefCount()
ing ever since being burned once by not doing it...I don't think it's strictly required here, tho.
编辑yzorg:
如果像这样扩展方法,您将更清楚地看到运行时行为:
If you augment the method like so, you'll see the runtime behavior more clearly:
public static IObservable<IList<T>> SlidingWindow<T>(
this IObservable<T> src,
int windowSize)
{
var feed = src.Publish().RefCount();
// (skip 0) + (skip 1) + (skip 2) + ... + (skip nth) => return as list
return Observable.Zip(
Enumerable.Range(0, windowSize)
.Select(skip =>
{
Console.WriteLine("Skipping {0} els", skip);
return feed.Skip(skip);
})
.ToArray());
}
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