5.6 KiB
title | description | menu | weight | flux/v0.x/tags | introduced | |||||||||
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derivative() function | `derivative()` computes the rate of change per unit of time between subsequent non-null records. |
|
101 |
|
0.7.0 |
derivative()
computes the rate of change per unit of time between subsequent
non-null records.
The function assumes rows are ordered by the _time
.
Output tables
The output table schema will be the same as the input table.
For each input table with n
rows, derivative()
outputs a table with
n - 1
rows.
Function type signature
(
<-tables: stream[A],
?columns: [string],
?initialZero: bool,
?nonNegative: bool,
?timeColumn: string,
?unit: duration,
) => stream[B] where A: Record, B: Record
{{% caption %}}For more information, see Function type signatures.{{% /caption %}}
Parameters
unit
Time duration used to calculate the derivative. Default is 1s
.
nonNegative
Disallow negative derivative values. Default is false
.
When true
, if a value is less than the previous value, the function
assumes the previous value should have been a zero.
columns
List of columns to operate on. Default is ["_value"]
.
timeColumn
Column containing time values to use in the calculation.
Default is _time
.
initialZero
Use zero (0) as the initial value in the derivative calculation
when the subsequent value is less than the previous value and nonNegative
is
true
. Default is false
.
tables
Input data. Default is piped-forward data (<-
).
Examples
- Calculate the non-negative rate of change per second
- Calculate the rate of change per second with null values
Calculate the non-negative rate of change per second
import "sampledata"
sampledata.int()
|> derivative(nonNegative: true)
{{< expand-wrapper >}} {{% expand "View example input and output" %}}
Input data
_time | _value | *tag |
---|---|---|
2021-01-01T00:00:00Z | -2 | t1 |
2021-01-01T00:00:10Z | 10 | t1 |
2021-01-01T00:00:20Z | 7 | t1 |
2021-01-01T00:00:30Z | 17 | t1 |
2021-01-01T00:00:40Z | 15 | t1 |
2021-01-01T00:00:50Z | 4 | t1 |
_time | _value | *tag |
---|---|---|
2021-01-01T00:00:00Z | 19 | t2 |
2021-01-01T00:00:10Z | 4 | t2 |
2021-01-01T00:00:20Z | -3 | t2 |
2021-01-01T00:00:30Z | 19 | t2 |
2021-01-01T00:00:40Z | 13 | t2 |
2021-01-01T00:00:50Z | 1 | t2 |
Output data
_time | _value | *tag |
---|---|---|
2021-01-01T00:00:10Z | 1.2 | t1 |
2021-01-01T00:00:20Z | t1 | |
2021-01-01T00:00:30Z | 1 | t1 |
2021-01-01T00:00:40Z | t1 | |
2021-01-01T00:00:50Z | t1 |
_time | _value | *tag |
---|---|---|
2021-01-01T00:00:10Z | t2 | |
2021-01-01T00:00:20Z | t2 | |
2021-01-01T00:00:30Z | 2.2 | t2 |
2021-01-01T00:00:40Z | t2 | |
2021-01-01T00:00:50Z | t2 |
{{% /expand %}} {{< /expand-wrapper >}}
Calculate the rate of change per second with null values
import "sampledata"
sampledata.int(includeNull: true)
|> derivative()
{{< expand-wrapper >}} {{% expand "View example input and output" %}}
Input data
_time | _value | *tag |
---|---|---|
2021-01-01T00:00:00Z | -2 | t1 |
2021-01-01T00:00:10Z | t1 | |
2021-01-01T00:00:20Z | 7 | t1 |
2021-01-01T00:00:30Z | t1 | |
2021-01-01T00:00:40Z | t1 | |
2021-01-01T00:00:50Z | 4 | t1 |
_time | _value | *tag |
---|---|---|
2021-01-01T00:00:00Z | t2 | |
2021-01-01T00:00:10Z | 4 | t2 |
2021-01-01T00:00:20Z | -3 | t2 |
2021-01-01T00:00:30Z | 19 | t2 |
2021-01-01T00:00:40Z | t2 | |
2021-01-01T00:00:50Z | 1 | t2 |
Output data
_time | _value | *tag |
---|---|---|
2021-01-01T00:00:10Z | t1 | |
2021-01-01T00:00:20Z | 0.45 | t1 |
2021-01-01T00:00:30Z | t1 | |
2021-01-01T00:00:40Z | t1 | |
2021-01-01T00:00:50Z | -0.1 | t1 |
_time | _value | *tag |
---|---|---|
2021-01-01T00:00:10Z | t2 | |
2021-01-01T00:00:20Z | -0.7 | t2 |
2021-01-01T00:00:30Z | 2.2 | t2 |
2021-01-01T00:00:40Z | t2 | |
2021-01-01T00:00:50Z | -0.9 | t2 |
{{% /expand %}} {{< /expand-wrapper >}}