I have need to collect the value of multiple datapoints and use them as a group. For a simplified example, I have X/Y points and want to graph them. But my data coming in is individual items. Each X value comes in and each Y value comes in via separate flow messages. The problem is that I may get multiple X values and the Y value may not change for an unknown period of time and is not reported at the same time. I need to send both values as a pair when an updated value is received. This is a simplified version of what I am after. I am wonder what my options are as I do not believe a Join node will work.
The join node is the right choice.
Set it to manual mode, leave everything default apart from entering 2 for the count field and ticking the checkbox for sending subsequent messages.
The key to making this work is ensuring that the input data has a valid topic. In your case the x value should have a topic of x and the y value should have a topic of y. If your data does not have a topic, you can simply add a topic using a change node before the join.
See this article in the cookbook for an example of how to join messages into one object.
Thank you, Steve. I thought I had tested this and was not getting what I wanted. Perhaps I had not checked the subsequent message option. I did misread the recipe where it states. "As we know there are three separate streams of messages to join, the node has been to configure to send on a message when it receives that number of parts." to mean that it needed to get 1 part from each and somehow missed the next paragraph. Reading it again, one might argue that perhaps that next paragraph should not be a second paragraph.
Just to note that when you have that checked you can determine which message has just been received by looking at msg.topic.
