216 lines
5.6 KiB
Markdown
216 lines
5.6 KiB
Markdown
---
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title: derivative() function
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description: >
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`derivative()` computes the rate of change per unit of time between subsequent
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non-null records.
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menu:
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flux_v0_ref:
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name: derivative
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parent: universe
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identifier: universe/derivative
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weight: 101
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flux/v0/tags: [transformations]
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introduced: 0.7.0
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---
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<!------------------------------------------------------------------------------
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IMPORTANT: This page was generated from comments in the Flux source code. Any
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edits made directly to this page will be overwritten the next time the
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documentation is generated.
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To make updates to this documentation, update the function comments above the
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function definition in the Flux source code:
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https://github.com/influxdata/flux/blob/master/stdlib/universe/universe.flux#L276-L286
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Contributing to Flux: https://github.com/influxdata/flux#contributing
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Fluxdoc syntax: https://github.com/influxdata/flux/blob/master/docs/fluxdoc.md
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------------------------------------------------------------------------------->
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`derivative()` computes the rate of change per unit of time between subsequent
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non-null records.
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The function assumes rows are ordered by the `_time`.
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#### Output tables
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The output table schema will be the same as the input table.
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For each input table with `n` rows, `derivative()` outputs a table with
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`n - 1` rows.
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##### Function type signature
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```js
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(
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<-tables: stream[A],
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?columns: [string],
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?initialZero: bool,
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?nonNegative: bool,
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?timeColumn: string,
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?unit: duration,
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) => stream[B] where A: Record, B: Record
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```
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{{% caption %}}
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For more information, see [Function type signatures](/flux/v0/function-type-signatures/).
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{{% /caption %}}
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## Parameters
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### unit
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Time duration used to calculate the derivative. Default is `1s`.
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### nonNegative
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Disallow negative derivative values. Default is `false`.
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When `true`, if a value is less than the previous value, the function
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assumes the previous value should have been a zero.
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### columns
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List of columns to operate on. Default is `["_value"]`.
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### timeColumn
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Column containing time values to use in the calculation.
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Default is `_time`.
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### initialZero
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Use zero (0) as the initial value in the derivative calculation
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when the subsequent value is less than the previous value and `nonNegative` is
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`true`. Default is `false`.
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### tables
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Input data. Default is piped-forward data (`<-`).
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## Examples
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- [Calculate the non-negative rate of change per second](#calculate-the-non-negative-rate-of-change-per-second)
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- [Calculate the rate of change per second with null values](#calculate-the-rate-of-change-per-second-with-null-values)
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### Calculate the non-negative rate of change per second
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```js
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import "sampledata"
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sampledata.int()
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|> derivative(nonNegative: true)
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```
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{{< expand-wrapper >}}
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{{% expand "View example input and output" %}}
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#### Input data
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:00Z | -2 | t1 |
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| 2021-01-01T00:00:10Z | 10 | t1 |
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| 2021-01-01T00:00:20Z | 7 | t1 |
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| 2021-01-01T00:00:30Z | 17 | t1 |
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| 2021-01-01T00:00:40Z | 15 | t1 |
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| 2021-01-01T00:00:50Z | 4 | t1 |
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:00Z | 19 | t2 |
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| 2021-01-01T00:00:10Z | 4 | t2 |
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| 2021-01-01T00:00:20Z | -3 | t2 |
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| 2021-01-01T00:00:30Z | 19 | t2 |
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| 2021-01-01T00:00:40Z | 13 | t2 |
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| 2021-01-01T00:00:50Z | 1 | t2 |
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#### Output data
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:10Z | 1.2 | t1 |
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| 2021-01-01T00:00:20Z | | t1 |
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| 2021-01-01T00:00:30Z | 1 | t1 |
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| 2021-01-01T00:00:40Z | | t1 |
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| 2021-01-01T00:00:50Z | | t1 |
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:10Z | | t2 |
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| 2021-01-01T00:00:20Z | | t2 |
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| 2021-01-01T00:00:30Z | 2.2 | t2 |
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| 2021-01-01T00:00:40Z | | t2 |
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| 2021-01-01T00:00:50Z | | t2 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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### Calculate the rate of change per second with null values
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```js
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import "sampledata"
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sampledata.int(includeNull: true)
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|> derivative()
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```
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{{< expand-wrapper >}}
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{{% expand "View example input and output" %}}
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#### Input data
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:00Z | -2 | t1 |
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| 2021-01-01T00:00:10Z | | t1 |
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| 2021-01-01T00:00:20Z | 7 | t1 |
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| 2021-01-01T00:00:30Z | | t1 |
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| 2021-01-01T00:00:40Z | | t1 |
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| 2021-01-01T00:00:50Z | 4 | t1 |
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:00Z | | t2 |
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| 2021-01-01T00:00:10Z | 4 | t2 |
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| 2021-01-01T00:00:20Z | -3 | t2 |
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| 2021-01-01T00:00:30Z | 19 | t2 |
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| 2021-01-01T00:00:40Z | | t2 |
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| 2021-01-01T00:00:50Z | 1 | t2 |
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#### Output data
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:10Z | | t1 |
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| 2021-01-01T00:00:20Z | 0.45 | t1 |
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| 2021-01-01T00:00:30Z | | t1 |
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| 2021-01-01T00:00:40Z | | t1 |
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| 2021-01-01T00:00:50Z | -0.1 | t1 |
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:10Z | | t2 |
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| 2021-01-01T00:00:20Z | -0.7 | t2 |
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| 2021-01-01T00:00:30Z | 2.2 | t2 |
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| 2021-01-01T00:00:40Z | | t2 |
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| 2021-01-01T00:00:50Z | -0.9 | t2 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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