Rx framework – IObservable<T>.Merge

In my previous post I used the IObservable<T>.Zip extension method in the Drag-and-Drop example, which takes two observable collections and runs a function over them to return a new observable collection of potentially a different type.

But what if you just want to simply merge the two observable collections into one stream? Well, Rx API has another extension method called Merge. To use it you can either invoke it as extension method:

var zs = xs.Merge(ys);

or you can invoke it as static method on more than two observable collections:

var zs = Observable.Merge(xs, ys, us, vs);

To use the Merge method, all the observable collections being merged need to be of the same type.

There are two things you should keep in mind:

1. OnCompleted is fired on the composite observable collection (zs) at the point the last OnCompleted is fired on any of the merged observable collections:

image

2. OnError is fired on the composite observable collection (zs) at the point the first OnError is fired on any of the merged observable collections, any subsequent values on the merged observable collection will not make it onto the composite collection:

image

Liked this article? Support me on Patreon and get direct help from me via a private Slack channel or 1-2-1 mentoring.
Subscribe to my newsletter


Hi, I’m Yan. I’m an AWS Serverless Hero and the author of Production-Ready Serverless.

I specialise in rapidly transitioning teams to serverless and building production-ready services on AWS.

Are you struggling with serverless or need guidance on best practices? Do you want someone to review your architecture and help you avoid costly mistakes down the line? Whatever the case, I’m here to help.

Hire me.


Check out my new course, Complete Guide to AWS Step Functions. In this course, we’ll cover everything you need to know to use AWS Step Functions service effectively. Including basic concepts, HTTP and event triggers, activities, callbacks, nested workflows, design patterns and best practices.

Get Your Copy