85 lines
2.3 KiB
Markdown
85 lines
2.3 KiB
Markdown
---
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title: covariance() function
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description: The `covariance()` function computes the covariance between two columns.
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aliases:
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- /influxdb/v2.0/reference/flux/functions/transformations/aggregates/covariance
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- /influxdb/v2.0/reference/flux/functions/built-in/transformations/aggregates/covariance/
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- /influxdb/v2.0/reference/flux/stdlib/built-in/transformations/aggregates/covariance/
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- /influxdb/v2.0/reference/flux/stdlib/built-in/transformations/covariance/
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- /influxdb/cloud/reference/flux/stdlib/built-in/transformations/covariance/
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menu:
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flux_0_x_ref:
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name: covariance
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parent: universe
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weight: 102
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flux/v0.x/tags: [transformations]
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related:
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- /flux/v0.x/stdlib/universe/cov/
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introduced: 0.7.0
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---
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The `covariance()` function computes the covariance between two columns.
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_**Output data type:** Float_
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```js
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covariance(columns: ["column_x", "column_y"], pearsonr: false, valueDst: "_value")
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```
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## Parameters
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### columns {data-type="array of strings"}
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({{< req >}}) A list of **two columns** on which to operate.
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### pearsonr {data-type="bool"}
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Normalized results to the Pearson R coefficient.
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Default is `false`.
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### valueDst {data-type="string"}
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The column into which the result will be placed.
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Defaults to `"_value"`.
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### tables {data-type="stream of tables"}
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Input data.
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Default is piped-forward data ([`<-`](/flux/v0.x/spec/expressions/#pipe-expressions)).
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## Examples
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The following example uses [`generate.from()`](/flux/v0.x/stdlib/generate/from/)
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to generate sample data and show how `covariance()` transforms data.
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```js
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import "generate"
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data = generate.from(count: 5, fn: (n) => n * n, start: 2021-01-01T00:00:00Z, stop: 2021-01-01T00:01:00Z)
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|> toFloat()
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|> map(fn: (r) => ({_time: r._time, x: r._value, y: r._value * r._value / 2.0}))
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data
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|> covariance(columns: ["x", "y"])
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```
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{{% expand "View input and output" %}}
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{{< flex >}}
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{{% flex-content %}}
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##### Input data
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| _time | x | y |
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| :------------------- | ---: | ----: |
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| 2021-01-01T00:00:00Z | 0.0 | 0.0 |
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| 2021-01-01T00:00:12Z | 1.0 | 0.5 |
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| 2021-01-01T00:00:24Z | 4.0 | 8.0 |
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| 2021-01-01T00:00:36Z | 9.0 | 40.5 |
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| 2021-01-01T00:00:48Z | 16.0 | 128.0 |
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{{% /flex-content %}}
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{{% flex-content %}}
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##### Output data
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| _value |
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| -----: |
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| 345.75 |
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{{% /flex-content %}}
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{{< /flex >}}
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{{% /expand %}}
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