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()