NonNaN

NonNaN is a term used in computing to denote numeric values that are not Not-a-Number (NaN). NaN is a special floating-point value defined by the IEEE 754 standard to represent undefined or unrepresentable results, such as 0 divided by 0 or the square root of a negative number. By contrast, nonNaN values are the regular numbers that participate in standard arithmetic and comparisons, including finite real numbers and, technically, infinities, which are not NaN.

In practice, identifying nonNaN values is important for data validation, numerical analysis, and error handling. Most programming languages provide a test for NaN, such as isnan or isNaN, and many offer a more precise variant like Number.isNaN in JavaScript or math.isnan in Python. A value is nonNaN when such tests indicate it is not NaN.

Behavior in arithmetic: NaN propagates through most operations, producing NaN as the result and often breaking standard comparisons; nonNaN arithmetic follows normal rules. Disentangling NaN from nonNaN is common in data pipelines: nonNaN filtering, imputation, or replacement with a valid numeric value.

In data science and related fields, distinguishing nonNaN values supports aggregations and statistics, as NaN values are typically excluded or handled separately. The concept underpins data cleaning, validation routines, and numerical algorithms that assume valid numeric input.

See also: NaN; IEEE 754; NaN propagation; data cleaning; finite numbers.