len

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.

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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.

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Usage

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Syntax

len(value)

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Parameters

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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.

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Use case examples

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

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

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

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

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List of related functions

• 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.