Thanks for the explanation I tried the above query for my use case but it’s giving the error data as an undefined identifier.
Can you tell what is the significance of data and why it’s giving the error?
I have used the max and min instead of the sum. is that the correct way?
from(bucket: “atlas_om”)

I tried this different method but it also giving an error as temp as an undefined identifier. I am not sure this is the correct way to do it.
from(bucket: “atlas_om”)
|> range(start: v.timeRangeStart, stop: v.timeRangeStop)
|> filter(fn: ® =>r._measurement == “measurement_name” and r._field == “column_name”)
|> filter(fn: ® => r[“host”] == “26e286667de4”)
|> reduce(
identitiy:{max_temp,min_temp,temp},
fn:(r,accumulator) => ({
max_temp: r._value.max(),
min_temp: r._value.min(),
temp: max_temp - min_temp
})
)
|> drop(columns: [“max_temp”,“min_temp”])
|> window(every: 1h)
|> yield(name: “differance”)

Hello @Ravikant_Gautam,
For me to help you I think it might be easier if you can explain what you’re trying to do?
It looks like you’re trying to find the difference between the max and min value in a table right for one field? or across all fields?

data = from(bucket: "my-bucket")
|> range(start: -5m)
|> filter(fn: (r) => r["_measurement"] == "cpu")
|> filter(fn: (r) => r["_field"] == "usage_system" or r["_field"] == "usage_user")
|> filter(fn: (r) => r["cpu"] == "cpu-total")
|> limit(n:3)
min =
data
|> min()
max =
data
|> max()
join(tables: {min: min, max: max}, on: ["_start"], method: "inner")
|> map(fn: (r) => ({ r with _value: r._value_max - r._value_min }))

The script above would calculate the max-min across fields.

Hello @Nam_Giang,
I wouldn’t recommend it because reduce() should really be reserved for custom aggregators. Using from() + range() + filter() + a bare aggregate or selector (like min or max) is a pushdown pattern for InfluxDB meaning that the transformation work is executed in storage rather than memory and is much more computationally efficient.
Please see:

But… here you go (I just wrapped in in a function):

minMaxMean = (tables=<-) =>
tables
|> reduce(
identity: {count: 0.0, sum: 0.0, min: 0.0, max: 0.0},
fn: (r, accumulator) => ({
count: accumulator.count + 1.0,
min: if accumulator.count == 0.0 then r._value else if r._value < accumulator.min then r._value else accumulator.min,
max: if accumulator.count == 0.0 then r._value else if r._value > accumulator.max then r._value else accumulator.max,
})
)

In my data I need to do the aggregate to find min/max/avg/sum of multiple fields. I’m not sure what’s the best option cause multiple unions are also not a good option in term of performance.

Hello @Nam_Giang,
Can you just use multiple yield statements? something like:

data = from
range
filter for multiple fields
// add group() where you want to find min/max/sum/avg across multiple fields
data
|> yield(name:"raw")
data
|> min()
|> yield(name:"min")
data
|> max)
|> yield(name:"max")
data
|> mean()
|> yield(name:"avg")
data
|> sum()
|> yield(name:"sum")