Create custom Flux functions
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Flux’s functional syntax lets you create custom functions. This guide walks through the basics of creating your own function.
- Function definition syntax
- Use piped-forward data in a custom function
- Define parameter defaults
- Define functions with scoped variables
Function definition syntax
The basic syntax for defining functions in Flux is as follows:
// Basic function definition syntax
functionName = (functionParameters) => functionOperationsfunctionName
The name used to call the function in your Flux script.
functionParameters
A comma-separated list of parameters passed into the function and used in its operations. Parameter defaults can be defined for each.
functionOperations
Operations and functions that manipulate the input into the desired output.
Basic function examples
Example square function
// Function definition
square = (n) => n * n
// Function usage
> square(n:3)
9Example multiply function
// Function definition
multiply = (x, y) => x * y
// Function usage
> multiply(x: 2, y: 15)
30Use piped-forward data in a custom function
Most Flux functions process piped-forward data.
To process piped-forward data, one of the function
parameters must capture the input tables using the <- pipe-receive expression.
In the example below, the tables parameter is assigned to the <- expression,
which represents all data piped-forward into the function.
tables is then piped-forward into other operations in the function definition.
functionName = (tables=<-) => tables |> functionOperationsPipe-forwardable function example
Multiply row values by x
The example below defines a multByX function that multiplies the _value column
of each row in the input table by the x parameter.
It uses the map() function
to modify each _value.
// Function definition
multByX = (tables=<-, x) => tables
|> map(fn: (r) => ({r with _value: r._value * x}))
// Function usage
from(bucket: "example-bucket")
|> range(start: -1m)
|> filter(fn: (r) => r._measurement == "mem" and r._field == "used_percent")
|> multByX(x: 2.0)Define parameter defaults
Use the = assignment operator to assign a default value to function parameters
in your function definition:
functionName = (param1=defaultValue1, param2=defaultValue2) => functionOperationDefaults are overridden by explicitly defining the parameter in the function call.
Example functions with defaults
Get a list of leaders
The example below defines a leaderBoard function that returns a limited number
of records sorted by values in specified columns.
It uses the sort() function
to sort records in either descending or ascending order.
It then uses the limit() function
to return a specified number of records from the sorted table.
// Function definition
leaderBoard = (tables=<-, limit=4, columns=["_value"], desc=true) => tables
|> sort(columns: columns, desc: desc)
|> limit(n: limit)
// Function usage
// Get the 4 highest scoring players
from(bucket: "example-bucket")
|> range(start: -1m)
|> filter(fn: (r) => r._measurement == "player-stats" and r._field == "total-points")
|> leaderBoard()
// Get the 10 shortest race times
from(bucket: "example-bucket")
|> range(start: -1m)
|> filter(fn: (r) => r._measurement == "race-times" and r._field == "elapsed-time")
|> leaderBoard(limit: 10, desc: false)Define functions with scoped variables
To create custom functions with variables scoped to the function, place your
function operations and variables inside of a block ({})
and use a return statement to return a specific variable.
functionName = (functionParameters) => {
exampleVar = "foo"
return exampleVar
}Example functions with scoped variables
Return an alert level based on a value
The following function uses conditional logic to return an alert level based on a numeric input value:
alertLevel = (v) => {
level = if float(v: v) >= 90.0 then
"crit"
else if float(v: v) >= 80.0 then
"warn"
else if float(v: v) >= 65.0 then
"info"
else
"ok"
return level
}
alertLevel(v: 87.3)
// Returns "warn"
Convert a HEX color code to a name
The following function converts a hexadecimal (HEX) color code to the equivalent HTML color name. The functions uses the Flux dictionary package to create a dictionary of HEX codes and their corresponding names.
import "dict"
hexName = (hex) => {
hexNames = dict.fromList(
pairs: [
{key: "#00ffff", value: "Aqua"},
{key: "#000000", value: "Black"},
{key: "#0000ff", value: "Blue"},
{key: "#ff00ff", value: "Fuchsia"},
{key: "#808080", value: "Gray"},
{key: "#008000", value: "Green"},
{key: "#00ff00", value: "Lime"},
{key: "#800000", value: "Maroon"},
{key: "#000080", value: "Navy"},
{key: "#808000", value: "Olive"},
{key: "#800080", value: "Purple"},
{key: "#ff0000", value: "Red"},
{key: "#c0c0c0", value: "Silver"},
{key: "#008080", value: "Teal"},
{key: "#ffffff", value: "White"},
{key: "#ffff00", value: "Yellow"},
],
)
name = dict.get(dict: hexNames, key: hex, default: "No known name")
return name
}
hexName(hex: "#000000")
// Returns "Black"
hexName(hex: "#8b8b8b")
// Returns "No known name"
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