ismap

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

Use the ismap function in APL to check whether a value is of the dynamic type and represents a mapping (also known as a dictionary, associative array, property bag, or object). A mapping consists of key-value pairs where keys are strings and values can be of any type. This function is especially useful when working with semi-structured data, such as logs or telemetry traces, where fields might dynamically contain arrays, objects, or scalar values.

Use ismap to:

• Filter records where a field is a map.
• Validate input types in heterogeneous data.
• Avoid runtime errors in downstream operations expecting map 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 typically work with field types implicitly and rarely check if a field is a dictionary. SPL lacks a direct equivalent to APL’s ismap, but you might perform similar validations using typeof checks or custom functions in eval.

Splunk example

| eval is_map=if(typeof(field) == "object", true, false)

ANSI SQL users

ANSI SQL does not natively support map types. If you use a platform that supports JSON or semi-structured data (such as PostgreSQL with jsonb, BigQuery with STRUCT, or Snowflake), you can simulate map checks using type inspection or schema introspection.

SQL example

SELECT
  CASE
    WHEN json_type(field) = 'object' THEN true
    ELSE false
  END AS is_map
FROM logs

Usage

Syntax

ismap(value)

Parameters

Name	Type	Description
value	any	The value to check for being a map.

Returns

Returns true if the value is a mapping (dictionary), otherwise returns false.

Example

Use ismap to find log entries where a dynamic field contains structured key-value pairs, such as metadata attached to HTTP requests.

Query

['sample-http-logs']
| extend is_structured = ismap(dynamic({"a":1, "b":2}))

Run in Playground

Output

_time	is_structured
2025-06-06T08:00:00Z	true

List of related functions

• isreal: Checks whether a value is a real number.
• isstring: Checks whether a value is a string. Use this for scalar string validation.

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