derivative() function

derivative() computes the rate of change per unit of time between subsequent non-null records.

The function assumes rows are ordered by the _time .

Output tables

The output table schema will be the same as the input table. For each input table with n rows, derivative() outputs a table with n - 1 rows.

Function type signature

(
    <-tables: stream[A],
    ?columns: [string],
    ?initialZero: bool,
    ?nonNegative: bool,
    ?timeColumn: string,
    ?unit: duration,
) => stream[B] where A: Record, B: Record

Parameters

unit

Time duration used to calculate the derivative. Default is 1s .

nonNegative

Disallow negative derivative values. Default is false .

When true , if a value is less than the previous value, the function assumes the previous value should have been a zero.

columns

List of columns to operate on. Default is ["_value"] .

timeColumn

Column containing time values to use in the calculation. Default is _time .

initialZero

Use zero (0) as the initial value in the derivative calculation when the subsequent value is less than the previous value and nonNegative is true . Default is false .

tables

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

Examples

• Calculate the non-negative rate of change per second
• Calculate the rate of change per second with null values

Calculate the non-negative rate of change per second

import "sampledata"
sampledata.int()
    |> derivative(nonNegative: true)

Calculate the rate of change per second with null values

import "sampledata"
sampledata.int(includeNull: true)
    |> derivative()