isnan

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.

Usage

Syntax

isnan(x)

Parameters

Returns

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

List of related functions

• 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.

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