Rx framework – IObservable<T>.CombineLatest

Check out my new course Learn you some Lambda best practice for great good! and learn the best practices for performance, cost, security, resilience, observability and scalability.

The IObservable<T>.CombineLatest extension method is very similar to IObservable<T>.Zip and IObservable<T>.Merge in that it combines two observable collections and returns a new one.

Unlike IObservable<T>.Merge, IObservable<T>.CombineLatest does not require the merged observable collections to be of the same type.

Like IObservable<T>.Zip, IObservable<T>.CombineLatest combines ‘pairs‘ of values from the two observable collections, but unlike Zip when a new value becomes available on one collection it does not wait till a new value to be available on the other collection, instead it takes whatever the latest value is from the other collection (provided there is one):

image

Again, like the Merge method, you can either invoke CombineLatest as an extension method:

var zs = xs.CombineLatest(ys, (a, b) => a + b);

or you can invoke it as static method:

var zs = Observable.CombineLatest(xs, ys, (a, b) => a + b);
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, Learn you some Lambda best practice for great good! In this course, you will learn best practices for working with AWS Lambda in terms of performance, cost, security, scalability, resilience and observability. Enrol now and enjoy a special preorder price of £9.99 (~$13).

Start Learning


Are you working with Serverless and looking for expert training to level-up your skills? Or are you looking for a solid foundation to start from? Look no further, register for my Production-Ready Serverless workshop to learn how to build production-grade Serverless applications!

Find a workshop near you