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

title	description	aliases	menu	weight	flux/v0.x/tags	introduced
keep() function	The `keep()` function returns a table containing only the specified columns.	/influxdb/v2.0/reference/flux/functions/transformations/keep /influxdb/v2.0/reference/flux/functions/built-in/transformations/keep/ /influxdb/v2.0/reference/flux/stdlib/built-in/transformations/keep/ /influxdb/cloud/reference/flux/stdlib/built-in/transformations/keep/	flux_0_x_ref name parent keep universe	102	transformations	0.7.0

The keep() function returns a table containing only the specified columns, ignoring all others. Only columns in the group key that are also specified in the keep() function will be kept in the resulting group key. It is the inverse of drop.

keep(columns: ["col1", "col2"])

// OR

keep(fn: (column) => column =~ /inodes*/)

Parameters

{{% note %}} Make sure fn parameter names match each specified parameter. To learn why, see Match parameter names. {{% /note %}}

columns

Columns that should be included in the resulting table. Cannot be used with fn.

fn

A predicate function which takes a column name as a parameter (column) and returns a boolean indicating whether or not the column should be included in the resulting table. Cannot be used with columns.

tables

Input data. Default is piped-forward data (<-).

Examples

{{% flux/sample-example-intro plural=true %}}

• 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 input and output" %}} {{< flex >}} {{% flex-content %}}

Input data

{{% flux/sample "int" %}}

{{% /flex-content %}} {{% flex-content %}}

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

{{% /flex-content %}} {{< /flex >}} {{% /expand %}} {{< /expand-wrapper >}}

Keep columns matching a predicate

import "sampledata"

sampledata.int()
    |> keep(fn: (column) => column =~ /^_?t/)

{{< expand-wrapper >}} {{% expand "View input and output" %}} {{< flex >}} {{% flex-content %}}

Input data

{{% flux/sample "int" %}}

{{% /flex-content %}} {{% flex-content %}}

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

{{% /flex-content %}} {{< /flex >}} {{% /expand %}} {{< /expand-wrapper >}}