107 lines
2.7 KiB
Markdown
107 lines
2.7 KiB
Markdown
---
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title: strings.hasPrefix() function
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description: >
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`strings.hasPrefix()` indicates if a string begins with a specified prefix.
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menu:
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flux_v0_ref:
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name: strings.hasPrefix
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parent: strings
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identifier: strings/hasPrefix
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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/strings/strings.flux#L260-L260
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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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`strings.hasPrefix()` indicates if a string begins with a specified prefix.
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##### Function type signature
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```js
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(prefix: string, v: string) => bool
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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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### v
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({{< req >}})
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String value to search.
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### prefix
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({{< req >}})
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Prefix to search for.
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## Examples
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### Filter based on the presence of a prefix in a column value
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```js
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import "sampledata"
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import "strings"
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sampledata.string()
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|> filter(fn: (r) => strings.hasPrefix(v: r._value, prefix: "smpl_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 | smpl_g9qczs |
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| 2021-01-01T00:00:10Z | t1 | smpl_0mgv9n |
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| 2021-01-01T00:00:20Z | t1 | smpl_phw664 |
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| 2021-01-01T00:00:30Z | t1 | smpl_guvzy4 |
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| 2021-01-01T00:00:40Z | t1 | smpl_5v3cce |
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| 2021-01-01T00:00:50Z | t1 | smpl_s9fmgy |
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| _time | *tag | _value |
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| -------------------- | ---- | ----------- |
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| 2021-01-01T00:00:00Z | t2 | smpl_b5eida |
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| 2021-01-01T00:00:10Z | t2 | smpl_eu4oxp |
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| 2021-01-01T00:00:20Z | t2 | smpl_5g7tz4 |
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| 2021-01-01T00:00:30Z | t2 | smpl_sox1ut |
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| 2021-01-01T00:00:40Z | t2 | smpl_wfm757 |
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| 2021-01-01T00:00:50Z | t2 | smpl_dtn2bv |
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#### Output data
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| _time | *tag | _value |
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| -------------------- | ---- | ----------- |
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| 2021-01-01T00:00:40Z | t1 | smpl_5v3cce |
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| _time | *tag | _value |
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| -------------------- | ---- | ----------- |
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| 2021-01-01T00:00:20Z | t2 | smpl_5g7tz4 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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