How to calculate difference between min and max with Flux?

1

Hello,
New to InfluxDB, I’m switching from MySql to influxDB 2.0
I’m so converting my mySQL queries to Flux.

I’m trying to calculate the difference between min and max of a range.

Here is what I tried:

datamin = from(bucket: "grafana")
  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
  |> filter(fn: (r) => r["_measurement"] == "history")
  |> filter(fn: (r) => r["_field"] == "value")
  |> min()
  |> aggregateWindow(every: 1s, fn: unique, createEmpty: false)
datamax = from(bucket: "grafana")
  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
  |> filter(fn: (r) => r["_measurement"] == "history")
  |> filter(fn: (r) => r["_field"] == "value")
  |> max()
  |> aggregateWindow(every: 1s, fn: unique, createEmpty: false)

Both independently are giving the correct values. Now I just want to show the difference but I don’t find the correct syntax. Below is the schematic idea of what I like to do

(datamin-datamax)
  |> yield()

Please help me for the correct syntax. Or maybe there is a more direct way to get this ?..
Thanks !

2

Hello @Heyjay,
Welcome!! Yes this is a common question. Learning Flux and Annotated CSV takes some adjustment, but once the flip switches it’s a lot easier.

data = from(bucket: "my-bucket")
  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)
  |> filter(fn: (r) => r["_measurement"] == "cpu")
  |> filter(fn: (r) => r["_field"] == "usage_system")
  |> filter(fn: (r) => r["cpu"] == "cpu-total")

min = data
  |> min()

max = data
  |> max()

join(tables: {min: min, max: max}, on: ["_start", "_field", "_start", "host", "_measurement"], method: "inner")
  |> map(fn: (r) => ({ r with _value: r._value_max - r._value_min }))

You can use a join() to subtract the two results. I join on all of the columns that are the same across the two tables to remove redundant columns.

1 Like
3

@Anaisdg thank you so much for the trick. This will help me a lot!

1 Like
4

@Heyjay,
Absolutely. Please let me know if you have any more questions :slight_smile: