> ## Documentation Index
> Fetch the complete documentation index at: https://axiom.co/docs/llms.txt
> Use this file to discover all available pages before exploring further.

<AgentInstructions>

## Submitting Feedback

If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback:

POST https://axiom.co/docs/feedback

```json
{
  "path": "/apl/scalar-functions/mathematical-functions/isnan",
  "feedback": "Description of the issue"
}
```

Only submit feedback when you have something specific and actionable to report.

</AgentInstructions>

# isnan

> This page explains how to use the isnan function in APL.

Use the `isnan` function in APL to check whether a numeric value is NaN (Not a Number). The function returns `true` when the value is NaN and `false` for all finite values and infinities.

`isnan` is essential for data quality work. Operations such as `log` of a negative number, `sqrt` of a negative number, or `0 / 0` produce NaN in APL. Use `isnan` to detect and filter these invalid values before aggregating, charting, or alerting on your data.

## 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.

<AccordionGroup>
  <Accordion title="Splunk SPL users">
    Splunk SPL includes the `isnan()` function, which works the same way as in APL: it returns `true` (1) when the value is NaN.

    <CodeGroup>
      ```sql Splunk example theme={null}
      | eval is_nan = isnan(value)
      ```

      ```kusto APL equivalent theme={null}
      ['sample-http-logs']
      | extend is_nan = isnan(value)
      ```
    </CodeGroup>
  </Accordion>

  <Accordion title="ANSI SQL users">
    Standard SQL does not define an `ISNAN()` function. In most dialects, `NaN` is not a concept; division by zero raises an error instead. However, some databases (such as PostgreSQL) do support `NaN` as a float value, and you check for it with `value = 'NaN'`.

    <CodeGroup>
      ```sql SQL example theme={null}
      SELECT CASE WHEN value = 'NaN' THEN 1 ELSE 0 END AS is_nan FROM logs
      ```

      ```kusto APL equivalent theme={null}
      ['sample-http-logs']
      | extend is_nan = isnan(value)
      ```
    </CodeGroup>
  </Accordion>
</AccordionGroup>

## Usage

### Syntax

```kusto theme={null}
isnan(x)
```

### Parameters

| Name | Type | Required | Description                 |
| ---- | ---- | -------- | --------------------------- |
| `x`  | real | Yes      | The numeric value to check. |

### Returns

`true` if `x` is NaN. `false` for finite values and infinity.

## List of related functions

* [isfinite](/apl/scalar-functions/mathematical-functions/isfinite): Returns `true` for values that are neither infinite nor NaN. Use it for a combined check covering all invalid float states.
* [isinf](/apl/scalar-functions/mathematical-functions/isinf): Returns `true` only for infinite values. Use it alongside `isnan` to cover all edge cases.
* [isint](/apl/scalar-functions/mathematical-functions/isint): Returns `true` for integer values. Use it for whole-number validation rather than float validity.
* [log](/apl/scalar-functions/mathematical-functions/log): Returns the natural logarithm. Use `isnan` to catch NaN results when `log` is applied to non-positive values.
* [sqrt](/apl/scalar-functions/mathematical-functions/sqrt): Returns the square root. Use `isnan` to detect NaN results from `sqrt` on negative inputs.