-- Descriptive statistics builtins: median, quantile, stdev, variance.
--
-- These are sample statistics: variance and stdev divide by N - 1 so they
-- match the convention used by R, NumPy (ddof=1), and most spreadsheet
-- functions (e.g. STDEV.S). Quantile uses linear interpolation between
-- adjacent values, with p clamped to [0, 1].
--
-- median xs:L n > n
-- quantile xs:L n p:n > n
-- stdev xs:L n > n
-- variance xs:L n > n
-- Median of an odd-length list is the middle value after sorting.
mid-odd>n;median [1, 2, 3, 4, 5]
-- Median of an even-length list is the mean of the two middle values.
mid-even>n;median [1, 2, 3, 4]
-- 90th percentile: linear interpolation at position p * (n - 1).
p90>n;quantile [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 0.9
-- Sample standard deviation of a small dataset (matches R's `sd`).
spread>n;stdev [2, 4, 4, 4, 5, 5, 7, 9]
-- run: mid-odd
-- out: 3
-- run: mid-even
-- out: 2.5
-- run: p90
-- out: 9.1
-- run: spread
-- out: 2.138089935299395