Filter one query by value of another

[Patrick Macdonald]

This seems a pretty simple thing to achieve so apologies if it's been answered here a hundred times before. 

If I have two metrics : 
"state"

"swap"

Each metric has records from different hosts, so they both have a "host" label. 

eg 

1. state, label {host="machineA"} value 0
2. state, label {host="machineB"} value 1

3. swap,  label {host="machineA"} value 1234

4. swap,  label {host="machineb"} value 123

I want to filter my graph of "swap" so that any hosts with a "state" value of "0" are removed/ignored. 

What's the trick?
Is the correct nomenclature for this "Filtering series A by series B"? (I'm still trying to get my head around the correct terminology to use).

Thanks in advance for your help.

Patrick

[David Leadbeater]

The most readable for a case like this is to use unless, something like:

swap unless on(host) state == 0

You can also turn the logic around, using and, e.g.:

swap and on(host) state > 0

David

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