docs-v2/content/flux/v0/stdlib/universe/keys.md

title	description	menu	weight	flux/v0/tags	introduced
keys() function	`keys()` returns the columns that are in the group key of each input table.	flux_v0_ref name parent identifier keys universe universe/keys	101	transformations	0.13.0

keys() returns the columns that are in the group key of each input table.

Each output table contains a row for each group key column label. A single group key column label is stored in the specified column for each row. All columns not in the group key are dropped.

Function type signature

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

{{% caption %}} For more information, see Function type signatures. {{% /caption %}}

Parameters

column

Column to store group key labels in. Default is _value.

tables

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

Examples

• Return group key columns for each input table
• Return all distinct group key columns in a single table
• Return group key columns as an array

Return group key columns for each input table

data
    |> keys()

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

Input data

*_field	*_measurement	*sensorID	_time	_value
co	airSensors	TLM0100	2021-09-08T14:21:57Z	0.31
co	airSensors	TLM0100	2021-09-08T14:22:07Z	0.295
co	airSensors	TLM0100	2021-09-08T14:22:17Z	0.314
co	airSensors	TLM0100	2021-09-08T14:22:27Z	0.313

*_field	*_measurement	*sensorID	_time	_value
humidity	airSensors	TLM0100	2021-09-08T14:21:57Z	36.03
humidity	airSensors	TLM0100	2021-09-08T14:22:07Z	36.07
humidity	airSensors	TLM0100	2021-09-08T14:22:17Z	36.1
humidity	airSensors	TLM0100	2021-09-08T14:22:27Z	36.12

*_field	*_measurement	*sensorID	_time	_value
temperature	airSensors	TLM0100	2021-09-08T14:21:57Z	70.84
temperature	airSensors	TLM0100	2021-09-08T14:22:07Z	70.86
temperature	airSensors	TLM0100	2021-09-08T14:22:17Z	70.89
temperature	airSensors	TLM0100	2021-09-08T14:22:27Z	70.85

Output data

*_field	*_measurement	*sensorID	_value
co	airSensors	TLM0100	_field
co	airSensors	TLM0100	_measurement
co	airSensors	TLM0100	sensorID

*_field	*_measurement	*sensorID	_value
humidity	airSensors	TLM0100	_field
humidity	airSensors	TLM0100	_measurement
humidity	airSensors	TLM0100	sensorID

*_field	*_measurement	*sensorID	_value
temperature	airSensors	TLM0100	_field
temperature	airSensors	TLM0100	_measurement
temperature	airSensors	TLM0100	sensorID

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

Return all distinct group key columns in a single table

data
    |> keys()
    |> keep(columns: ["_value"])
    |> distinct()

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

Input data

*_field	*_measurement	*sensorID	_time	_value
co	airSensors	TLM0100	2021-09-08T14:21:57Z	0.31
co	airSensors	TLM0100	2021-09-08T14:22:07Z	0.295
co	airSensors	TLM0100	2021-09-08T14:22:17Z	0.314
co	airSensors	TLM0100	2021-09-08T14:22:27Z	0.313

*_field	*_measurement	*sensorID	_time	_value
humidity	airSensors	TLM0100	2021-09-08T14:21:57Z	36.03
humidity	airSensors	TLM0100	2021-09-08T14:22:07Z	36.07
humidity	airSensors	TLM0100	2021-09-08T14:22:17Z	36.1
humidity	airSensors	TLM0100	2021-09-08T14:22:27Z	36.12

*_field	*_measurement	*sensorID	_time	_value
temperature	airSensors	TLM0100	2021-09-08T14:21:57Z	70.84
temperature	airSensors	TLM0100	2021-09-08T14:22:07Z	70.86
temperature	airSensors	TLM0100	2021-09-08T14:22:17Z	70.89
temperature	airSensors	TLM0100	2021-09-08T14:22:27Z	70.85

Output data

_value
_field
_measurement
sensorID

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

Return group key columns as an array

1. Use keys() to replace the _value column with the group key labels.
2. Use findColumn() to return the _value column as an array.

import "sampledata"

sampledata.int()
    |> keys()
    |> findColumn(fn: (key) => true, column: "_value")// Returns [tag]