185 lines
4.8 KiB
Markdown
185 lines
4.8 KiB
Markdown
---
|
|
title: keep() function
|
|
description: >
|
|
`keep()` returns a stream of tables containing only the specified columns.
|
|
menu:
|
|
flux_v0_ref:
|
|
name: keep
|
|
parent: universe
|
|
identifier: universe/keep
|
|
weight: 101
|
|
flux/v0/tags: [transformations]
|
|
introduced: 0.7.0
|
|
---
|
|
|
|
<!------------------------------------------------------------------------------
|
|
|
|
IMPORTANT: This page was generated from comments in the Flux source code. Any
|
|
edits made directly to this page will be overwritten the next time the
|
|
documentation is generated.
|
|
|
|
To make updates to this documentation, update the function comments above the
|
|
function definition in the Flux source code:
|
|
|
|
https://github.com/influxdata/flux/blob/master/stdlib/universe/universe.flux#L1251-L1254
|
|
|
|
Contributing to Flux: https://github.com/influxdata/flux#contributing
|
|
Fluxdoc syntax: https://github.com/influxdata/flux/blob/master/docs/fluxdoc.md
|
|
|
|
------------------------------------------------------------------------------->
|
|
|
|
`keep()` returns a stream of tables containing only the specified columns.
|
|
|
|
Columns in the group key that are not specified in the `columns` parameter or
|
|
identified by the `fn` parameter are removed from the group key and dropped
|
|
from output tables. `keep()` is the inverse of `drop()`.
|
|
|
|
##### Function type signature
|
|
|
|
```js
|
|
(<-tables: stream[A], ?columns: [string], ?fn: (column: string) => bool) => stream[B] where A: Record, B: Record
|
|
```
|
|
|
|
{{% caption %}}
|
|
For more information, see [Function type signatures](/flux/v0/function-type-signatures/).
|
|
{{% /caption %}}
|
|
|
|
## Parameters
|
|
|
|
### columns
|
|
|
|
Columns to keep in output tables. Cannot be used with `fn`.
|
|
|
|
|
|
|
|
### fn
|
|
|
|
Predicate function that takes a column name as a parameter (column) and
|
|
returns a boolean indicating whether or not the column should be kept in
|
|
output tables. Cannot be used with `columns`.
|
|
|
|
|
|
|
|
### tables
|
|
|
|
Input data. Default is piped-forward data (`<-`).
|
|
|
|
|
|
|
|
|
|
## Examples
|
|
|
|
- [Keep a list of columns](#keep-a-list-of-columns)
|
|
- [Keep columns matching a predicate](#keep-columns-matching-a-predicate)
|
|
|
|
### Keep a list of columns
|
|
|
|
```js
|
|
import "sampledata"
|
|
|
|
sampledata.int()
|
|
|> keep(columns: ["_time", "_value"])
|
|
|
|
```
|
|
|
|
{{< expand-wrapper >}}
|
|
{{% expand "View example input and output" %}}
|
|
|
|
#### Input data
|
|
|
|
| _time | _value | *tag |
|
|
| -------------------- | ------- | ---- |
|
|
| 2021-01-01T00:00:00Z | -2 | t1 |
|
|
| 2021-01-01T00:00:10Z | 10 | t1 |
|
|
| 2021-01-01T00:00:20Z | 7 | t1 |
|
|
| 2021-01-01T00:00:30Z | 17 | t1 |
|
|
| 2021-01-01T00:00:40Z | 15 | t1 |
|
|
| 2021-01-01T00:00:50Z | 4 | t1 |
|
|
|
|
| _time | _value | *tag |
|
|
| -------------------- | ------- | ---- |
|
|
| 2021-01-01T00:00:00Z | 19 | t2 |
|
|
| 2021-01-01T00:00:10Z | 4 | t2 |
|
|
| 2021-01-01T00:00:20Z | -3 | t2 |
|
|
| 2021-01-01T00:00:30Z | 19 | t2 |
|
|
| 2021-01-01T00:00:40Z | 13 | t2 |
|
|
| 2021-01-01T00:00:50Z | 1 | t2 |
|
|
|
|
|
|
#### Output data
|
|
|
|
| _time | _value |
|
|
| -------------------- | ------- |
|
|
| 2021-01-01T00:00:00Z | -2 |
|
|
| 2021-01-01T00:00:10Z | 10 |
|
|
| 2021-01-01T00:00:20Z | 7 |
|
|
| 2021-01-01T00:00:30Z | 17 |
|
|
| 2021-01-01T00:00:40Z | 15 |
|
|
| 2021-01-01T00:00:50Z | 4 |
|
|
| 2021-01-01T00:00:00Z | 19 |
|
|
| 2021-01-01T00:00:10Z | 4 |
|
|
| 2021-01-01T00:00:20Z | -3 |
|
|
| 2021-01-01T00:00:30Z | 19 |
|
|
| 2021-01-01T00:00:40Z | 13 |
|
|
| 2021-01-01T00:00:50Z | 1 |
|
|
|
|
{{% /expand %}}
|
|
{{< /expand-wrapper >}}
|
|
|
|
### Keep columns matching a predicate
|
|
|
|
```js
|
|
import "sampledata"
|
|
|
|
sampledata.int()
|
|
|> keep(fn: (column) => column =~ /^_?t/)
|
|
|
|
```
|
|
|
|
{{< expand-wrapper >}}
|
|
{{% expand "View example input and output" %}}
|
|
|
|
#### Input data
|
|
|
|
| _time | _value | *tag |
|
|
| -------------------- | ------- | ---- |
|
|
| 2021-01-01T00:00:00Z | -2 | t1 |
|
|
| 2021-01-01T00:00:10Z | 10 | t1 |
|
|
| 2021-01-01T00:00:20Z | 7 | t1 |
|
|
| 2021-01-01T00:00:30Z | 17 | t1 |
|
|
| 2021-01-01T00:00:40Z | 15 | t1 |
|
|
| 2021-01-01T00:00:50Z | 4 | t1 |
|
|
|
|
| _time | _value | *tag |
|
|
| -------------------- | ------- | ---- |
|
|
| 2021-01-01T00:00:00Z | 19 | t2 |
|
|
| 2021-01-01T00:00:10Z | 4 | t2 |
|
|
| 2021-01-01T00:00:20Z | -3 | t2 |
|
|
| 2021-01-01T00:00:30Z | 19 | t2 |
|
|
| 2021-01-01T00:00:40Z | 13 | t2 |
|
|
| 2021-01-01T00:00:50Z | 1 | t2 |
|
|
|
|
|
|
#### Output data
|
|
|
|
| _time | *tag |
|
|
| -------------------- | ---- |
|
|
| 2021-01-01T00:00:00Z | t1 |
|
|
| 2021-01-01T00:00:10Z | t1 |
|
|
| 2021-01-01T00:00:20Z | t1 |
|
|
| 2021-01-01T00:00:30Z | t1 |
|
|
| 2021-01-01T00:00:40Z | t1 |
|
|
| 2021-01-01T00:00:50Z | t1 |
|
|
|
|
| _time | *tag |
|
|
| -------------------- | ---- |
|
|
| 2021-01-01T00:00:00Z | t2 |
|
|
| 2021-01-01T00:00:10Z | t2 |
|
|
| 2021-01-01T00:00:20Z | t2 |
|
|
| 2021-01-01T00:00:30Z | t2 |
|
|
| 2021-01-01T00:00:40Z | t2 |
|
|
| 2021-01-01T00:00:50Z | t2 |
|
|
|
|
{{% /expand %}}
|
|
{{< /expand-wrapper >}}
|