Can I increment a (possibly null) context variable in a change node?

General
1

I am trying to count the number of each node type in flows.json. Not difficult using a function but I would like to do it without writing javascript code.

So read the file and split the resulting array gives me one message per node with the node type in msg.payload.type

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How can I use a change node to increment a flow counter eg flow.messagecounts["function"] += 1 ?

I have tried this but I think because flow.messagecounts[msg.payload.type] is initially undefined, the increment never works?

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2

You could use a Switch to test for undefined, and a change node to set it to zero if so. Then increment it in the next node.

I expect someone will come up with a one-liner JSONata expression to count them.

3

You can use the $sum() trick

$sum([$$.increment]) + 1
4

I thought it might be possible to do the whole thing in JSONata, feeding in the flows file and ending up with the total node count for each type.

5

Yes I am sure it is, and save it all to context

6

That's a good thought! It's a json file so I am sure that would be possible.

But what I am actually doing is revising my personal recipe for embedding awk in a template node. The Node-red version is for comparison.
I only thought of flows.json because it's there and has records spanning multiple lines.
A magical sentence of jsonata will only reinforce the idea that awk is last century technology!

I'm having trouble with @Colin's switch node suggestion. something odd is going on. More investigation needed.

7

JSONata will indeed have trouble incrementing an undefined value... but you can protect your expression by using this ternary:

increment ? increment + 1 : 1

I know you don't want to write "function" code, but just for reference you can easily group/count the entire flow using this JSONata expression:

payload { type: $count($) }
8

I think this flow does the same thing, but using the localhost:1880/admin/flows url to get the flow JSON (instead of trying to locate, read, and parse the flows.json file).

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[{"id":"e14a6f161d1bebd0","type":"inject","z":"3729ccee2b11666e","name":"go","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":110,"y":100,"wires":[["95d9639c08ce944b"]]},{"id":"30d599f146373c72","type":"change","z":"3729ccee2b11666e","name":"flow: messagecounts","rules":[{"t":"set","p":"payload","pt":"msg","to":"payload { type: $count($) }","tot":"jsonata"},{"t":"set","p":"messagecounts","pt":"flow","to":"payload","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":480,"y":100,"wires":[["7e3ed51935ab040b"]]},{"id":"7e3ed51935ab040b","type":"debug","z":"3729ccee2b11666e","name":"type: count","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":670,"y":100,"wires":[]},{"id":"95d9639c08ce944b","type":"http request","z":"3729ccee2b11666e","name":"GET /admin/flows","method":"GET","ret":"obj","paytoqs":"ignore","url":"http://localhost:1880/admin/flows","tls":"","persist":false,"proxy":"","insecureHTTPParser":false,"authType":"","senderr":false,"headers":[],"x":270,"y":100,"wires":[["30d599f146373c72"]]}]

Since the entire flows.json is processed into a summary object, I just replace the whole flow variable.

9

That's the answer!
So using that I have

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[{"id":"112a69ed01730f17","type":"inject","z":"3378d78bb37c052e","name":"go","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":90,"y":60,"wires":[["d51cde875f4b5a0a"]]},{"id":"b23439ad43e95d6e","type":"file in","z":"3378d78bb37c052e","name":"flows.json","filename":".node-red/flows.json","filenameType":"str","format":"utf8","chunk":false,"sendError":false,"encoding":"none","allProps":false,"x":480,"y":60,"wires":[["69782fbbccdc6b91"]]},{"id":"69782fbbccdc6b91","type":"json","z":"3378d78bb37c052e","name":"","property":"payload","action":"","pretty":false,"x":610,"y":60,"wires":[["cb63f29ecd2aaa90"]]},{"id":"cb63f29ecd2aaa90","type":"split","z":"3378d78bb37c052e","name":"","splt":"\\n","spltType":"str","arraySplt":1,"arraySpltType":"len","stream":false,"addname":"","x":730,"y":60,"wires":[["ba5835d2d3c68141"]]},{"id":"d51cde875f4b5a0a","type":"change","z":"3378d78bb37c052e","name":"delete flow.messagecounts","rules":[{"t":"set","p":"messagecounts","pt":"flow","to":"{\"ui_spacer\": 2}","tot":"json"}],"action":"","property":"","from":"","to":"","reg":false,"x":280,"y":60,"wires":[["b23439ad43e95d6e"]]},{"id":"ba5835d2d3c68141","type":"change","z":"3378d78bb37c052e","name":"Count each node type","rules":[{"t":"set","p":"increment","pt":"msg","to":"messagecounts[msg.payload.type]","tot":"flow"},{"t":"set","p":"increment","pt":"msg","to":"increment ? increment + 1 : 1","tot":"jsonata"},{"t":"set","p":"messagecounts[msg.payload.type]","pt":"flow","to":"increment","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":140,"y":120,"wires":[["9893a5a9708d4e00"]]},{"id":"9893a5a9708d4e00","type":"switch","z":"3378d78bb37c052e","name":"Last msg part?","property":"parts.count","propertyType":"msg","rules":[{"t":"eq","v":"parts.index + 1","vt":"jsonata"}],"checkall":"true","repair":false,"outputs":1,"x":340,"y":120,"wires":[["6c23c7047b383eb2"]]},{"id":"b121e56aabb8829a","type":"debug","z":"3378d78bb37c052e","name":"debug 482","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":750,"y":120,"wires":[]},{"id":"6c23c7047b383eb2","type":"change","z":"3378d78bb37c052e","name":"Final counts to payload","rules":[{"t":"set","p":"payload","pt":"msg","to":"messagecounts","tot":"flow"}],"action":"","property":"","from":"","to":"","reg":false,"x":550,"y":120,"wires":[["b121e56aabb8829a"]]}]

None of the other approaches worked for me, sorry guys :thinking:
I appreciate the suggestions though.

10

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