Axiom Docs

Use the len function in APL (Axiom Processing Language) to determine the length of a string or the number of elements in an array. This function is useful when you want to filter, sort, or analyze data based on the size of a value—whether that’s the number of characters in a request URL or the number of cities associated with a user. Use len when you need to:

Measure string lengths (for example, long request URIs).
Count elements in dynamic arrays (such as tags or multi-value fields).
Create conditional expressions based on the length of values.

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 often use the len function within eval or where expressions to determine string length or array size. In APL, len works similarly, but is used as a standalone scalar function.

... | eval uri_length=len(uri)

['sample-http-logs']
| extend uri_length = len(uri)

ANSI SQL users

In ANSI SQL, you use LENGTH() for strings and CARDINALITY() for arrays. In APL, len handles both cases—string and array—depending on the input type.

SELECT LENGTH(uri) AS uri_length FROM http_logs;

['sample-http-logs']
| extend uri_length = len(uri)

Usage

Syntax

len(value)

Parameters

Name	Type	Description
value	string or array	The input to measure—either a string or an array.

Returns

If value is a string, returns the number of characters.
If value is an array, returns the number of elements.
Returns null if the input is null.

Use case examples

Log analysis
OpenTelemetry traces
Security logs

Use len to find requests with long URIs, which might indicate poorly designed endpoints or potential abuse.Query

['sample-http-logs']
| extend uri_length = len(uri)
| where uri_length > 100
| project _time, id, uri, uri_length

Run in PlaygroundOutput

_time	id	uri	uri_length
2025-06-18T12:34:00Z	user123	/api/products/search?query=…	132
2025-06-18T12:35:00Z	user456	/download/file/very/long/path/…	141

The query filters logs for URIs longer than 100 characters and displays their lengths.

Use len to identify traces with IDs of unexpected length, which might indicate instrumentation issues or data inconsistencies.Query

['otel-demo-traces']
| extend trace_id_length = len(trace_id)
| summarize count() by trace_id_length

Run in PlaygroundOutput

trace_id_length	count
32	4987
16	12

The query summarizes trace IDs by their lengths to find unexpected values.

Use len to analyze request methods and flag unusually short ones (e.g., malformed logs or attack vectors).Query

['sample-http-logs']
| extend method_length = len(method)
| where method_length < 3
| project _time, id, method, method_length

Run in PlaygroundOutput

_time	id	method	method_length
2025-06-18T13:10:00Z	user789	P	1
2025-06-18T13:12:00Z	user222	G	1

The query finds suspicious or malformed request methods that are unusually short.

array_length: Returns the number of elements in an array. Use this when working specifically with arrays.
array_slice: Returns a subarray like array_extract, but supports negative indexing.
array_concat: Joins arrays end-to-end. Use before or after slicing arrays with array_extract.

Introduction

APL

MPL

len

For users of other query languages

Usage

Syntax

Parameters

Returns

Use case examples

​For users of other query languages

​Usage

​Syntax

​Parameters

​Returns

​Use case examples

​List of related functions

For users of other query languages

Usage

Syntax

Parameters

Returns

Use case examples

List of related functions