fix(variance): return NaN for sample variance of single-element collection - #180
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…ction Population variance of a single observation is 0 (no spread), but sample variance is mathematically undefined because the denominator n-1 equals 0. The prior guard short-circuited both cases with 0, silently producing incorrect results for the sample case. Tests are split into separate population and sample cases to make the distinction explicit, and two constant-value two-element cases are added to cover the zero-spread boundary. Fixes: #179
JimmyMAndersson
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Population variance of a single observation is 0 (no spread), but sample variance is mathematically undefined because the denominator n-1 equals 0. The prior guard short-circuited both cases with 0, silently producing incorrect results for the sample case.
Tests are split into separate population and sample cases to make the distinction explicit, and two constant-value two-element cases are added to cover the zero-spread boundary.
Fixes: #179