204 lines
5.4 KiB
Markdown
204 lines
5.4 KiB
Markdown
---
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title: quantile() function
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description: >
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`quantile()` returns rows from each input table with values that fall within a
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specified quantile or returns the row with the value that represents the
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specified quantile.
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menu:
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flux_0_x_ref:
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name: quantile
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parent: universe
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identifier: universe/quantile
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weight: 101
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flux/v0.x/tags: [transformations, aggregates, selectors]
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introduced: 0.24.0
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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#L1951-L1959
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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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`quantile()` returns rows from each input table with values that fall within a
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specified quantile or returns the row with the value that represents the
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specified quantile.
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`quantile()` supports columns with float values.
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### Function behavior
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`quantile()` acts as an aggregate or selector transformation depending on the
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specified `method`.
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- **Aggregate**: When using the `estimate_tdigest` or `exact_mean` methods,
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`quantile()` acts as an aggregate transformation and outputs the average of
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non-null records with values that fall within the specified quantile.
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- **Selector**: When using the `exact_selector` method, `quantile()` acts as
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a selector selector transformation and 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],
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q: float,
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?column: string,
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?compression: float,
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?method: string,
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) => stream[A] where A: Record
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```
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{{% caption %}}For more information, see [Function type signatures](/flux/v0.x/function-type-signatures/).{{% /caption %}}
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## Parameters
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### column
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Column to use to compute the quantile. Default is `_value`.
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### q
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({{< req >}})
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Quantile to compute. Must be between `0.0` and `1.0`.
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### method
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Computation method. Default is `estimate_tdigest`.
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**Avaialable methods**:
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- **estimate_tdigest**: Aggregate method that uses a
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[t-digest data structure](https://github.com/tdunning/t-digest) to
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compute an accurate quantile estimate on large data sources.
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- **exact_mean**: Aggregate method that takes the average of the two
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points closest to the quantile value.
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- **exact_selector**: Selector method that returns the row with the value
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for which at least `q` points are less than.
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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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- [Quantile as an aggregate](#quantile-as-an-aggregate)
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- [Quantile as a selector](#quantile-as-a-selector)
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### Quantile as an aggregate
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```js
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import "sampledata"
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sampledata.float()
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|> quantile(q: 0.99, method: "estimate_tdigest")
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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 | 17.53 |
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| *tag | _value |
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| ---- | ------- |
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| t2 | 19.85 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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### Quantile as a selector
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```js
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import "sampledata"
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sampledata.float()
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|> 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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