Merging Observables - system.reactive

Question

Here we have a Observable Sequence... in .NET using Rx.
var aSource = new Subject<int>();
var bSource = new Subject<int>();
var paired = Observable
.Merge(aSource, bSource)
.GroupBy(i => i).SelectMany(g => g.Buffer(2).Take(1));
paired.Subscribe(g => Console.WriteLine("{0}:{1}", g.ElementAt(0), g.ElementAt(1)));
aSource.OnNext(4);
bSource.OnNext(1);
aSource.OnNext(2);
bSource.OnNext(5);
aSource.OnNext(3);
bSource.OnNext(3);
aSource.OnNext(5);
bSource.OnNext(2);
aSource.OnNext(1);
bSource.OnNext(4);
Output:
3:3
5:5
2:2
1:1
4:4
We will get events every time a pair of numbers arrive with the same id.
Perfect! Just what i want.
Groups of two, paired by value.
Next question....
How to get a selectmany/buffer for sequences of values.
So 1,2,3,4,5 arrives at both aSource and bSource via OnNext(). Then fire ConsoleWriteLine() for 1-5. Then when 2,3,4,5,6 arrives, we get another console.writeline(). Any clues anyone?
Immediately, the Rx forum suggests looking at .Window()
http://introtorx.com/Content/v1.0.10621.0/17_SequencesOfCoincidence.html
Which on the surface looks perfect. In my case i need a window of value 4, in this case.
Where in the query sequence does it belong to get this effect?
var paired = Observable.Merge(aSource, bSource).GroupBy(i => i).SelectMany(g => g.Buffer(2).Take(1));
Output
1,2,3,4,5 : 1,2,3,4,5
2,3,4,5,6 : 2,3,4,5,6
Regards,
Daniel

Answer 1

Assuming events arrive randomly at the sources, use my answer to "Reordering events with Reactive Extensions" to get the events in order.
Then use Observable.Buffer to create a sliding buffer:
// get this using the OrderedCollect/Sort in the referenced question
IObservable<int> orderedSource;
// then subscribe to this
orderedSource.Buffer(5, 1);

Answer 2

Here is an extension method that fires when it has n inputs of the same ids.
public static class RxExtension
{
public static IObservable<TSource> MergeBuffer<TSource>(this IObservable<TSource> source, Func<TSource, int> keySelector, Func<IList<TSource>,TSource> mergeFunction, int bufferCount)
{
return Observable.Create<TSource>(o => {
var buffer = new Dictionary<int, IList<TSource>>();
return source.Subscribe<TSource>(i =>
{
var index = keySelector(i);
if (buffer.ContainsKey(index))
{
buffer[index].Add(i);
}
else
{
buffer.Add(index, new List<TSource>(){i});
}
if (buffer.Count==bufferCount)
{
o.OnNext(mergeFunction(buffer[index]));
buffer.Remove(index);
}
});
});
}
}
Calling the extension.
mainInput = Observable.Merge(inputNodes.ToArray()).MergeBuffer<NodeData>(x => x.id, x => MergeData(x), 1);