Compare two payloads

[lourdes98]

Hi! I'm using the 16.17.0 version of Node.JS and Node-RED v2.2.2.

I want to read a value coming from payload, save it and compare it with the next one. Both comes from the same node.

Then, execute a routine inside of a function node.

Can ypu help me with this+?

[craigcurtin]

As they are distinct messages you need to save one somewhere until the second one comes in

You have two choices - you can use a context variable (read up on flow context variables) or you can try and use the join node before your function node - however if both values are coming from the same node it may be difficult to differentiate them properly for the join node to work

Craig

[MecatronicaMADE]

Hi @lourdes98 and welcome to Node-RED community, as @craigcurtin said, you can use variables to store your values, I share you a flow with a little example:

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In this example I compare two payloads, simulating that comes from the same node. I did this example with numbers, but can work with other kinds...

I hope it helps you!!

[jbudd]

@lourdes98

I want to read a value coming from payload, save it and compare it with the next one.

If this comparison is a relatively simple one, for example if a numeric payload changes by 10% or more, then the Filter node can do the job, no need to store the payload in a variable.

[lourdes98]

Thank you @MecatronicaMADE ,You really helped me

[Steve-Mcl]

Where possible, context should be the last choice. I say this due to the async nature of node-red and unexpected results you can get when multiple values are passing within quick succession.

Here is a very similar flow using the join node instead (no context)...