125 lines
3.2 KiB
Markdown
125 lines
3.2 KiB
Markdown
---
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title: math.log2() function
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description: >
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`math.log2()` is a function returns the binary logarithm of `x`.
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menu:
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flux_v0_ref:
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name: math.log2
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parent: math
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identifier: math/log2
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weight: 101
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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/math/math.flux#L1493-L1493
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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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`math.log2()` is a function returns the binary logarithm of `x`.
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##### Function type signature
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```js
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(x: float) => 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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### x
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({{< req >}})
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the value used in the operation.
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## Examples
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- [Return the binary logarithm of a value](#return-the-binary-logarithm-of-a-value)
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- [Use math.log2 in map](#use-mathlog2-in-map)
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### Return the binary logarithm of a value
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```js
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import "math"
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math.log2(x: 3.14)// 1.6507645591169022
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```
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### Use math.log2 in map
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```js
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import "sampledata"
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import "math"
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sampledata.float()
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|> map(fn: (r) => ({r with _value: math.log2(x: r._value)}))
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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 | _value | *tag |
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| -------------------- | ------------------ | ---- |
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| 2021-01-01T00:00:00Z | NaN | t1 |
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| 2021-01-01T00:00:10Z | 3.4489009511451276 | t1 |
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| 2021-01-01T00:00:20Z | 2.877744249949002 | t1 |
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| 2021-01-01T00:00:30Z | 4.131754090984813 | t1 |
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| 2021-01-01T00:00:40Z | 3.9288440367125674 | t1 |
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| 2021-01-01T00:00:50Z | 2.1473066987802936 | t1 |
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| _time | _value | *tag |
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| -------------------- | ------------------ | ---- |
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| 2021-01-01T00:00:00Z | 4.3110671022555955 | t2 |
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| 2021-01-01T00:00:10Z | 2.3132458517875616 | t2 |
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| 2021-01-01T00:00:20Z | NaN | t2 |
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| 2021-01-01T00:00:30Z | 4.305240965954483 | t2 |
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| 2021-01-01T00:00:40Z | 3.792855352362489 | t2 |
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| 2021-01-01T00:00:50Z | 0.8953026213333067 | t2 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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