Prevent sending duplicate values downstream

[ganymedes]

Hey everyone

I’m coming from a Node-RED background and recently started diving into n8n — absolutely loving the flexibility so far!

One thing I used quite a lot in Node-RED was the RBE node (“Report by Exception”). It basically filters messages so that only changed values pass through — super useful when dealing with sensor data, API polling, or anything that doesn’t need to send duplicates.

Use case example:

Let’s say I’m polling a temperature sensor every 30 seconds. I only want to take action (like send a webhook or update a dashboard) if the temperature has actually changed — otherwise, it’s just noise.

So my question is:

How would you implement RBE-style logic in n8n?

*Is there a built-in way to compare the current value with the previous one?

• Would this require storing state somewhere (like in a static data variable, or external DB)?
• Has anyone built a custom function or node for this?

Any tips, workflows, or patterns you’ve found helpful would be amazing!

Thanks in advance

Cheers Mike

[barn4k]

hello @ganymedes

There are multiple approaches:

1. you can use Remove Duplicates node

2. You can store old values somewhere (e.g. google sheet/db/etc) and compare the values with it with the Merge node (simple equal compare) or with Compare Dataset node (complex compare based on multiple fields).