182 lines
4.5 KiB
Markdown
182 lines
4.5 KiB
Markdown
---
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title: drop() function
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description: >
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`drop()` removes specified columns from a table.
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menu:
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flux_v0_ref:
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name: drop
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parent: universe
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identifier: universe/drop
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weight: 101
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flux/v0/tags: [transformations]
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introduced: 0.7.0
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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#L462-L465
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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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`drop()` removes specified columns from a table.
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Columns are specified either through a list or a predicate function.
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When a dropped column is part of the group key, it is removed from the key.
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If a specified column is not present in a table, the function returns an error.
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##### Function type signature
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```js
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(<-tables: stream[A], ?columns: [string], ?fn: (column: string) => bool) => stream[B] where A: Record, B: Record
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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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### columns
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List of columns to remove from input tables. Mutually exclusive with `fn`.
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### fn
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Predicate function with a `column` parameter that returns a boolean
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value indicating whether or not the column should be removed from input tables.
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Mutually exclusive with `columns`.
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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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- [Drop a list of columns](#drop-a-list-of-columns)
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- [Drop columns matching a predicate](#drop-columns-matching-a-predicate)
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### Drop a list of columns
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```js
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import "sampledata"
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sampledata.int()
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|> drop(columns: ["_time", "tag"])
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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 | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:00Z | -2 | t1 |
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| 2021-01-01T00:00:10Z | 10 | t1 |
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| 2021-01-01T00:00:20Z | 7 | t1 |
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| 2021-01-01T00:00:30Z | 17 | t1 |
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| 2021-01-01T00:00:40Z | 15 | t1 |
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| 2021-01-01T00:00:50Z | 4 | t1 |
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:00Z | 19 | t2 |
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| 2021-01-01T00:00:10Z | 4 | t2 |
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| 2021-01-01T00:00:20Z | -3 | t2 |
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| 2021-01-01T00:00:30Z | 19 | t2 |
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| 2021-01-01T00:00:40Z | 13 | t2 |
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| 2021-01-01T00:00:50Z | 1 | t2 |
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#### Output data
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| _value |
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| ------- |
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| -2 |
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| 10 |
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| 7 |
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| 17 |
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| 15 |
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| 4 |
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| 19 |
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| 4 |
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| -3 |
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| 19 |
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| 13 |
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| 1 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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### Drop columns matching a predicate
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```js
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import "sampledata"
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sampledata.int()
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|> drop(fn: (column) => column =~ /^t/)
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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 | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:00Z | -2 | t1 |
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| 2021-01-01T00:00:10Z | 10 | t1 |
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| 2021-01-01T00:00:20Z | 7 | t1 |
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| 2021-01-01T00:00:30Z | 17 | t1 |
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| 2021-01-01T00:00:40Z | 15 | t1 |
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| 2021-01-01T00:00:50Z | 4 | t1 |
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:00Z | 19 | t2 |
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| 2021-01-01T00:00:10Z | 4 | t2 |
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| 2021-01-01T00:00:20Z | -3 | t2 |
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| 2021-01-01T00:00:30Z | 19 | t2 |
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| 2021-01-01T00:00:40Z | 13 | t2 |
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| 2021-01-01T00:00:50Z | 1 | t2 |
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#### Output data
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| _time | _value |
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| -------------------- | ------- |
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| 2021-01-01T00:00:00Z | -2 |
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| 2021-01-01T00:00:10Z | 10 |
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| 2021-01-01T00:00:20Z | 7 |
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| 2021-01-01T00:00:30Z | 17 |
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| 2021-01-01T00:00:40Z | 15 |
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| 2021-01-01T00:00:50Z | 4 |
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| 2021-01-01T00:00:00Z | 19 |
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| 2021-01-01T00:00:10Z | 4 |
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| 2021-01-01T00:00:20Z | -3 |
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| 2021-01-01T00:00:30Z | 19 |
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| 2021-01-01T00:00:40Z | 13 |
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| 2021-01-01T00:00:50Z | 1 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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