205 lines
5.6 KiB
Markdown
205 lines
5.6 KiB
Markdown
---
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title: experimental.quantile() function
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description: >
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`experimental.quantile()` returns non-null records with values in the `_value` column that
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fall within the specified quantile or represent the specified quantile.
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menu:
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flux_v0_ref:
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name: experimental.quantile
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parent: experimental
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identifier: experimental/quantile
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weight: 101
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flux/v0/tags: [transformations, aggregates, selectors]
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introduced: 0.107.0
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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/experimental/experimental.flux#L884-L889
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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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`experimental.quantile()` returns non-null records with values in the `_value` column that
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fall within the specified quantile or represent the specified quantile.
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The `_value` column must contain float values.
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## Computation methods and behavior
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`experimental.quantile()` behaves like an **aggregate function** or a
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**selector function** depending on the `method` parameter.
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The following computation methods are available:
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##### estimate_tdigest
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An aggregate method that uses a [t-digest data structure](https://github.com/tdunning/t-digest)
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to compute an accurate quantile estimate on large data sources.
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When used, `experimental.quantile()` outputs non-null records with values
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that fall within the specified quantile.
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##### exact_mean
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An aggregate method that takes the average of the two points closest to the quantile value.
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When used, `experimental.quantile()` outputs non-null records with values
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that fall within the specified quantile.
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##### exact_selector
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A selector method that returns the data point for which at least `q` points are less than.
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When used, `experimental.quantile()` outputs the non-null record with the
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value that represents the specified quantile.
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##### Function type signature
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```js
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(
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<-tables: stream[{A with _value: float}],
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q: float,
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?compression: float,
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?method: string,
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) => stream[{A with _value: float}]
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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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### q
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({{< req >}})
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Quantile to compute (`[0 - 1]`).
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### method
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Computation method. Default is `estimate_tdigest`.
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**Supported methods**:
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- estimate_tdigest
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- exact_mean
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- exact_selector
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### compression
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Number of centroids to use when compressing the dataset.
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Default is `1000.0`.
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A larger number produces a more accurate result at the cost of increased
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memory requirements.
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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 values in the 50th percentile of each input table](#return-values-in-the-50th-percentile-of-each-input-table)
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- [Return a value representing the 50th percentile of each input table](#return-a-value-representing-the-50th-percentile-of-each-input-table)
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### Return values in the 50th percentile of each input table
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```js
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import "experimental"
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import "sampledata"
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sampledata.float()
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|> experimental.quantile(q: 0.5)
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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 | *tag | _value |
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| -------------------- | ---- | ------- |
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| 2021-01-01T00:00:00Z | t1 | -2.18 |
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| 2021-01-01T00:00:10Z | t1 | 10.92 |
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| 2021-01-01T00:00:20Z | t1 | 7.35 |
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| 2021-01-01T00:00:30Z | t1 | 17.53 |
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| 2021-01-01T00:00:40Z | t1 | 15.23 |
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| 2021-01-01T00:00:50Z | t1 | 4.43 |
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| _time | *tag | _value |
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| -------------------- | ---- | ------- |
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| 2021-01-01T00:00:00Z | t2 | 19.85 |
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| 2021-01-01T00:00:10Z | t2 | 4.97 |
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| 2021-01-01T00:00:20Z | t2 | -3.75 |
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| 2021-01-01T00:00:30Z | t2 | 19.77 |
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| 2021-01-01T00:00:40Z | t2 | 13.86 |
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| 2021-01-01T00:00:50Z | t2 | 1.86 |
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#### Output data
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| *tag | _value |
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| ---- | ------- |
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| t1 | 9.135 |
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| *tag | _value |
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| ---- | ------- |
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| t2 | 9.415 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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### Return a value representing the 50th percentile of each input table
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```js
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import "experimental"
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import "sampledata"
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sampledata.float()
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|> experimental.quantile(q: 0.5, method: "exact_selector")
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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 | *tag | _value |
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| -------------------- | ---- | ------- |
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| 2021-01-01T00:00:00Z | t1 | -2.18 |
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| 2021-01-01T00:00:10Z | t1 | 10.92 |
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| 2021-01-01T00:00:20Z | t1 | 7.35 |
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| 2021-01-01T00:00:30Z | t1 | 17.53 |
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| 2021-01-01T00:00:40Z | t1 | 15.23 |
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| 2021-01-01T00:00:50Z | t1 | 4.43 |
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| _time | *tag | _value |
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| -------------------- | ---- | ------- |
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| 2021-01-01T00:00:00Z | t2 | 19.85 |
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| 2021-01-01T00:00:10Z | t2 | 4.97 |
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| 2021-01-01T00:00:20Z | t2 | -3.75 |
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| 2021-01-01T00:00:30Z | t2 | 19.77 |
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| 2021-01-01T00:00:40Z | t2 | 13.86 |
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| 2021-01-01T00:00:50Z | t2 | 1.86 |
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#### Output data
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| _time | *tag | _value |
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| -------------------- | ---- | ------- |
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| 2021-01-01T00:00:20Z | t1 | 7.35 |
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| _time | *tag | _value |
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| -------------------- | ---- | ------- |
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| 2021-01-01T00:00:10Z | t2 | 4.97 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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