119 lines
2.9 KiB
Markdown
119 lines
2.9 KiB
Markdown
---
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title: stddev() function
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description: >
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`stddev()` returns the standard deviation of non-null values in a specified column.
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menu:
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flux_v0_ref:
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name: stddev
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parent: universe
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identifier: universe/stddev
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weight: 101
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flux/v0/tags: [transformations, aggregates]
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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#L2611-L2614
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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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`stddev()` returns the standard deviation of non-null values in a specified column.
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##### Function type signature
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```js
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(<-tables: stream[A], ?column: string, ?mode: string) => 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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### column
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Column to operate on. Default is `_value`.
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### mode
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Standard deviation mode or type of standard deviation to calculate.
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Default is `sample`.
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**Available modes:**
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- **sample**: Calculate the sample standard deviation where the data is
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considered part of a larger population.
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- **population**: Calculate the population standard deviation where the
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data is considered a population of its own.
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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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### Return the standard deviation of values in each table
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```js
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import "sampledata"
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sampledata.int()
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|> stddev()
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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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| *tag | _value |
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| ---- | ----------------- |
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| t1 | 7.063993204979744 |
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| *tag | _value |
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| ---- | ----------------- |
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| t2 | 9.474527252938094 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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