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.

​
Usage

​
Syntax

len(value)

​
Parameters

NameTypeDescription
valuestring or arrayThe 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

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
_timeiduriuri_length
2025-06-18T12:34:00Zuser123/api/products/search?query=…132
2025-06-18T12:35:00Zuser456/download/file/very/long/path/…141
The query filters logs for URIs longer than 100 characters and displays their lengths.
  • 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.