Reference · Math

math.isnan

math.isnan(num) -> bool

What it does

Whether a float is NaN, "not a number", as Python's math.isnan. NaN comes out of arithmetic that has no answer, inf - inf or float("nan"), and it is the one value that is not equal to itself, so x == x is false for it and math.isnan is the way to catch it.

Examples

let nan = float("nan")print(math.isnan(nan), math.isnan(1), math.isnan(2.5))print(nan == nan, math.isnan(nan))

true false falsefalse true

Edge cases

• Infinity is not NaN.
• inf - inf, 0.0 * inf and sqrt(-1) are NaN; math.sqrt(-1) is a runtime error instead, so it never gives one.
• 0 / 0 is a runtime error, division by zero, not NaN.

let inf = float("inf")print(math.isnan(inf), math.isnan(inf - inf), math.isnan(0.0 * inf), math.isnan(sqrt(-1)))

false true true true

Errors

An argument that is not a number is a runtime error, not an error value: null is refused rather than reported as NaN.

print(math.isnan(null))

line 1: `math.isnan` expects a number as argument 1, got null

Chaining

In a pipeline the number comes first. Dropping the NaNs before a statistic:

print(sqrt(-1) | math.isnan)print([1.0, sqrt(-1), 3.0] | filter((x) => !math.isnan(x)) | stats.mean)

true2.0

See also

math.isfinite, math.isinf, math.isclose, sqrt

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