Define custom functions

Flux’s functional syntax lets you define custom functions. Learn the basics of creating your own functions.

Function definition syntax

The basic syntax for defining functions in Flux is as follows:

// Basic function definition syntax
functionName = (functionParameters) => functionBody

functionName: Name to use to execute the function.
functionParameters: Comma-separated list of parameters passed into the function.
functionBody: Operations on function parameters.

Define parameter defaults

Use the = assignment operator to assign a default value to function parameters in your function definition:

functionName = (param1=defaultVal1, param2=defaultVal2) => functionBody

Defaults are overridden by explicitly defining the parameter in the function call. Parameters without default values are considered required parameters.

Custom function examples

Square a number

Multiple two values

Calculate n to the p power (with default parameters)

Create a custom transformation

A transformation is a function that takes a stream of tables as input, operates on the input, and then outputs a new stream of tables.

The pipe-forward operator (|>) pipes data from the previous identifier or function forward into a transformation. To use piped-forward data, assign a function parameter to the pipe-receive operator (<-).

In the following example, the function x() receives piped-forwarded data and assigns it to the t parameter. In the function body, t is piped forward into other operations to generate output.

x = (t=<-) => t |> //...

Custom transformation examples

Multiply values by x

srcID	_field	_value
t1a	foo	1.2
t1a	foo	3.4
t1a	foo	5.6

srcID	_field	_value
t2b	foo	0.8
t2b	foo	1.9
t2b	foo	2.7

srcID	_field	_value
t1a	foo	2.4
t1a	foo	6.8
t1a	foo	11.2

srcID	_field	_value
t2b	foo	1.6
t2b	foo	3.8
t2b	foo	5.4

Calculate speed

id	elapsed	distance
t1	1h15m	101
t2	1h32m	138
t3	56m	112

id	elapsed	distance	speed
t1	1h15m	101	88.8 mph
t2	1h32m	138	90 mph
t3	56m	112	120 mph

Define functions with scoped variables

To create custom functions with variables scoped to the function,

Enclose your function body in a block ({}).
Use a return statement to return a specific variable.

functionName = (param) => {
    exampleVar = "foo"

    return exampleVar
}

Example functions with scoped variables

Return an alert level based on a value

Convert a HEX color code to a name

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Define custom functions

On this page:

Function definition syntax

Define parameter defaults

Custom function examples

Create a custom transformation

Custom transformation examples

Multiply values by x

Function definition

Example usage

Given the following input data:

The example above returns:

Calculate speed

Function definition

Example usage

Given the following input data:

The example above returns:

Define functions with scoped variables

Example functions with scoped variables

Return an alert level based on a value

Convert a HEX color code to a name

Support and feedback

The future of Flux

InfluxDB v3 enhancements and InfluxDB Clustered is now generally available

InfluxDB v3 performance and features

InfluxDB Clustered general availability

Define custom functions

On this page:

Function definition syntax

Define parameter defaults

Custom function examples

Create a custom transformation

Custom transformation examples

Multiply values by x

Function definition

Example usage

Given the following input data:

The example above returns:

Calculate speed

Function definition

Example usage

Given the following input data:

The example above returns:

Define functions with scoped variables

Example functions with scoped variables

Return an alert level based on a value

Convert a HEX color code to a name

Related

Support and feedback

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Custom

Thank you for your feedback!

The future of Flux

InfluxDB v3 enhancements and InfluxDB Clustered is now generally available

InfluxDB v3 performance and features

InfluxDB Clustered general availability