Storing float from MQTT > Influx

Hi all,
I have a MQTT topic that seems to be storing a float as a string. Example:
It is a reading from a electricity consumption monitor and stores 33.2 or 45.3 in MQTT as a string. I have no control of how its doing this.

I have a simple flow in node red that does:
MQTT Electricity Topic > Influx (Measurement)

The issue is it creates a measurement with the following Field Keys:
Time , Value (as string)

I went into the Influx CLI and created my own measurement with Time, Value (Float) but of course (and I expected this) when I reroute the flow to that new measurement, I get the following error:

Error: A 400 Bad Request error occurred: {"error":"partial write: field type conflict: input field \"value\" on measurement \"B14023Device0Study\" is type string, already exists as type float dropped=1"

Which tells me of course that the flow is trying to pass a string value to a field key pairing that requires float.

My question

How I am thinking of it is that in the flow there is going to be a need for me to convert the value coming out of the MQTT topic as string to float, then pass that value to the influx db measurement I created with the field key pairing with the float.


  1. Is my thinking correct
  2. What would be the easiest way to do this conversion of the string value out of the MQTT topic into a float before I pass it to the influx node to write into that measurement? From the research I found this article Convert I can pretty much make out how to convert it. Just want to check my thinking on point 1 first.

Would really appreciate the guidance.

Insert a function node before the influx node and in there put

msg.payload = Number(msg.payload)
return msg

Feed it into a debug node before you connect it to the influx node to check it now shows it as a number, not a string.

Thank you very much @Colin I will test that. Thank you once again I really do appreciate it.

Or try this:

Yes, much better. I didn't think that worked if the data is a string containing just a number, but it does. If ever the string is not a valid number (or other valid json) then it generates an error, but that can be caught by a Catch node if necessary.

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