series_subtract

This page explains how to use the series_subtract function in APL.

The series_subtract function performs element-wise subtraction between two numeric dynamic arrays (series). Each element in the first series is subtracted by the corresponding element at the same position in the second series.

You can use series_subtract when you need to compute differences between two time-series datasets. This is particularly useful for calculating deltas, deviations from baselines, changes over time, or comparing metrics between different groups or time periods.

For users of other query languages

If you come from other query languages, this section explains how to adjust your existing queries to achieve the same results in APL.

Splunk SPL users

In Splunk SPL, you typically use the eval command with the subtraction operator to calculate differences between fields. In APL, series_subtract operates on entire arrays at once, performing element-wise subtraction efficiently.

Splunk example

... | eval difference=value1 - value2

ANSI SQL users

In SQL, you subtract values using the - operator on individual columns. In APL, series_subtract performs element-wise subtraction across entire arrays stored in single columns.

SQL example

SELECT value1 - value2 AS difference
FROM measurements;

Usage

Syntax

series_subtract(series1, series2)

Parameters

Parameter	Type	Description
series1	dynamic	A dynamic array of numeric values (minuend).
series2	dynamic	A dynamic array of numeric values (subtrahend).

Returns

A dynamic array where each element is the result of subtracting the corresponding element of series2 from series1. If the arrays have different lengths, the shorter array is extended with null values.

Use case examples

Log analysis

In log analysis, you can use series_subtract to calculate the difference between current and baseline request durations, helping identify performance degradations.

Query

['sample-http-logs']
| summarize current = make_list(req_duration_ms) by ['geo.city']
| extend baseline = dynamic([50, 55, 48, 52, 49])
| extend delta = series_subtract(current, baseline)
| take 5

Run in Playground

Output

geo.city	current	baseline	delta
Seattle	[60, 65, 58, 62, 59]	[50, 55, 48, 52, 49]	[10, 10, 10, 10, 10]
Portland	[45, 50, 43, 47, 44]	[50, 55, 48, 52, 49]	[-5, -5, -5, -5, -5]

This query calculates the difference between current request durations and baseline values, showing performance changes per city.

List of related functions

• series_multiply: Performs element-wise multiplication of two series. Use when you need to multiply rather than subtract.
• series_abs: Returns the absolute value of each element. Use after subtraction to get magnitude of differences.
• series_stats: Returns statistical summary of a series. Use to analyze the result of subtraction operations.
• series_sign: Returns the sign of each element. Use after subtraction to determine direction of changes.