How to only pass through a certain part of an array?

General
1

Hi

I have a node sending data from a energy-meter.
The data that i recieve is delivered like this.
Delivery 1: an array of data,
Delivery 2. a given value (1 line of the array)
Delivery 3: a given value (1 line of the array)

I am using a function node to extract a certain value frome the array:

var o = msg.payload
msg.payload = o.volt_L3 / 10
return msg;

The issue is sthat "delivery nr 2 & 3" does not have the array, therfore the results is "NaN".

The value i try to extract is passed on to a smart-house-system. The "NaN" value is therfore translated in to "0" in the smart-house-system.

What is best-pracsis for only extracting data from the msg. that has the full array, and skipp/not pass on the data from the msg. that doesnt have the full array.

2

That will not work if msg.payload is an array. Perhaps you mean a javascript object. I think you had better feed the messages into a debug node and show us what you have actually got.

What node are you using for getting the data?

3

Are your values coming into the function from separate wires? You might need a join node

Show us your flow.

4

You can filter your payload with a switch node, checking if the payload contains an array.

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5

Hi

This is the debug frome the node ( AMD decoder)

image
image433×796 21.4 KB

As you can see from the picture, every 3. messages is the "whole object", the 2 other messages contains onlye the vale "act_pow_pos"

Its all beeing "picked upp" trough a USB-adapter..

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image893×175 6.44 KB

6

Ok then it is not an array which you need to pick out - so you need to filter on a specific property.

[{"id":"3f247e651403fc6f","type":"switch","z":"cb05e14b.326a9","name":"","property":"payload.meter_ID","propertyType":"msg","rules":[{"t":"nnull"}],"checkall":"true","repair":false,"outputs":1,"x":620,"y":1580,"wires":[[]]}]

So only those messages will pass with a valid meter_ID

7

Maybe i was a bit unclear.. in my example i would like to only extra the value corresponding to: volt_L1.
If i use a change node to "extract" the value, the messeages that dosent have the value for volt_L1 returnes as "undefined".

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8

OK - then use the switch - I posted before and check for payload.volt_L1 not null.

9

Yes, sorry. This solves it.
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10

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