Skip to main content
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.
Splunk SPL includes the isnan() function, which works the same way as in APL: it returns true (1) when the value is NaN.
| eval is_nan = isnan(value)
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'.
SELECT CASE WHEN value = 'NaN' THEN 1 ELSE 0 END AS is_nan FROM logs

​
Usage

​
Syntax

isnan(x)

​
Parameters

NameTypeRequiredDescription
xrealYesThe numeric value to check.

​
Returns

true if x is NaN. false for finite values and infinity.
  • isfinite: Returns true for values that are neither infinite nor NaN. Use it for a combined check covering all invalid float states.
  • isinf: Returns true only for infinite values. Use it alongside isnan to cover all edge cases.
  • isint: Returns true for integer values. Use it for whole-number validation rather than float validity.
  • log: Returns the natural logarithm. Use isnan to catch NaN results when log is applied to non-positive values.
  • sqrt: Returns the square root. Use isnan to detect NaN results from sqrt on negative inputs.