Extending "last" value to now

InfluxDB 2
1

Hello. I’m new to InfluxDB. I’m using it with OpenHAB for data persistence of my home devices along with Grafana to plot some of the values. Specifically, I’m trying to make a graph of my living room lights, which are a dimmer. OpenHAB only saves the state of the switch when it changes. How can I write a query that propagates the latest value to the current time?

I don’t want to calculate values in-between either because it doesn’t make sense; Meaning a value of 100% at 3:30 and value of 10% at 4:00 should not generate a point of 55% at 3:45 because at 3:45, the lights were still at 100%.

Looking at this screenshot, you can see the line does not extend all the way to the right (ie: “now”). I know absolutely nothing about Flux language. I slapped this query from the example provided by Grafana and a tiny bit of exploring in the Influx UI.

Screen Shot 2022-07-23 at 1.18.53 PM
Screen Shot 2022-07-23 at 1.18.53 PM2756×1870 304 KB 

from(bucket: "home_metrics")
  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
  |> filter(fn: (r) => r["_measurement"] == "LivingroomLights_Dimmer" and r._field == "value")

Any help here would be appreciated! Thanks!

2

Hi @utdrmac Welcome to the Community Forum!

Your question sounds similar to a recent post (which BTW remains open). Take a look at the last comment over there with the square wave pix. So I guess you’d like the last reported value to be propagated forward?

3

Hello @utdrmac,
My first thought is to do:

import "experimental/array"

array.from(rows: [{foo: "bar", baz: 21.2, _time: 2022-07-30T00:00:00Z}, {foo: "bar", baz: 23.8, _time: 2022-07-31T00:00:00Z}])
|> range(start: 2022-07-29T00:00:00Z, stop: 2022-08-02T00:00:00Z)
|> aggregateWindow(every: 1d, fn: first, column: "baz")
|> group()
|> fill(usePrevious: true)