isstring

Use the isstring function to determine whether a value is of type string. This function is especially helpful when working with heterogeneous datasets where field types are not guaranteed, or when ingesting data from sources with loosely structured or mixed schemas.

You can use isstring to:

• Filter rows based on whether a field is a string.
• Validate and clean data before applying string functions.
• Avoid runtime errors in queries that expect specific data types.

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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

isstring(value)

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Parameters

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Returns

A bool value that is true if the input value is of type string, false otherwise.

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Use case example

Use isstring to filter rows where the HTTP status code is a valid string.

Query

['sample-http-logs']
| extend is_string = isstring(status)
| where is_string

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Output

This query filters out logs where the status field is stored as a string, which can help filter out ingestion issues or schema inconsistencies.

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List of related functions

• ismap: Checks whether a value is of the dynamic type and represents a mapping.
• isreal: Checks whether a value is a real number.