docs-v2/content/flux/v0.x/stdlib/universe/keep.md

title	description	menu	weight	flux/v0.x/tags	introduced
keep() function	`keep()` returns a stream of tables containing only the specified columns.	flux_0_x_ref name parent identifier keep universe universe/keep	101	transformations	0.7.0

keep() returns a stream of tables containing only the specified columns.

Columns in the group key that are not specifed 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

(<-tables: stream[A], ?columns: [string], ?fn: (column: string) => bool) => stream[B] where A: Record, B: Record

{{% caption %}}For more information, see 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 columns matching a predicate

Keep a list of columns

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

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 >}}