series_less

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

The series_less function compares two numeric arrays element by element and returns a Boolean array. Each position in the result contains true if the element in the first array is less than the corresponding element in the second array, and false otherwise.

You use series_less when you want to evaluate trends across sequences of numeric values. It’s especially useful in time series analysis, anomaly detection, or comparing metrics side by side. For example, you can check if response times are decreasing compared to a baseline or if one service consistently performs faster than another.

Usage

Syntax

APL

series_less(array1, array2)

Parameters

Parameter	Type	Description
`array1`	array	The first array of numeric values.
`array2`	array	The second array of numeric values. Must have the same length as `array1`.

Returns

An array of Boolean values. Each element is true if the corresponding element in array1 is less than the element in array2, otherwise false.

Use case examples

You want to check whether the average request duration in each city is less than a fixed threshold of 150 milliseconds.

Query

APLRun in Playground

['sample-http-logs']
| take 50
| make-series city_avg = avg(req_duration_ms) on _time step 1h by ['geo.city']
| extend threshold = dynamic([150, 150, 150])
| extend is_less = series_less(city_avg, threshold)

Output

geo.city	city_avg	threshold	is_less
London	[120, 90, 100]	[150, 150, 150]	[true, true, true]
Paris	[180, 200, 190]	[150, 150, 150]	[false, false, false]

This query shows whether each city’s request duration stays below a 150 ms threshold at each time step.

You want to detect if failed requests in each country are consistently less than successful requests.