Ternary operator in Influx flux - influxdb

Question

I am doing a join in influx to get the first and last values for a interval and then getting the difference.
Preset = 600
FirstValues = from(bucket: "Historian/oneday")
|> range(start: dashboardTime)
|> filter(fn: (r) =>
r._measurement == "TestMeasurement" and
r._field =="Value" and
r.Loc=="TXS"
)
|>window(every:15m)
|>first()
LastValues = from(bucket: "Historian/oneday")
|> range(start: dashboardTime)
|> filter(fn: (r) =>
r._measurement == "TestMeasurement" and
r._field =="Value" and
r.Loc=="TXS"
)
|>window(every:15m)
|>last()
CombinedValues = join (
tables:{first:FirstValues,last:LastValues},
on:["_stop","_start"]
)
totaliser = CombinedValues
|>map(fn: (r) => ({
_time: r._start,
//Want to do this, r._value_first < r._value_last ? Preset : r._value_first
_value: r._value_first - r._value_last
}))
totaliser
|>window(every:inf)
This works fine till the time difference returns a positive number.
But if the 1st value from join returns is less than 2nd value , I want to update that with a perset value.
Ex:
Preset = 600
totaliser = CombinedValues
|>map(fn: (r) => ({
_time: r._start,
//Want to do this, r._value_first < r._value_last ? Preset : r._value_first
_value: r._value_first - r._value_last
}))

Answer 1

Conditional logic is pretty new to Flux, but it does exist. Currently there is only if, else if, and else:
// Pattern
if <condition> then <action> else <alternative-action>
// Example
if color == "green" then "008000" else "ffffff"
But this will be expanded with time.
https://v2.docs.influxdata.com/v2.0/query-data/guides/conditional-logic/