NIKX-Tech/numx

stats: skewness and kurtosis

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#80 opened on Jul 11, 2026

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enhancementgood first issue

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Description

Add numx_stats_skewness and numx_stats_kurtosis to the stats module.

numx_stats_variance already uses Welford's online algorithm for numerical stability, see the note in #59 and #57's PR about why naive summation is avoided in this codebase, follow the same care here (an online algorithm extending Welford's, e.g. tracking higher moments incrementally, is preferable to a naive sum-based formula).

Follow CONTRIBUTING.md exactly: full Doxygen header, NULL-checks, numx_status_t return, all four deliverables (header, impl, test, docs page).

Contributor guide

Research direction
Study Welford's online algorithm for variance and extend it to compute third and fourth central moments incrementally. Implement functions numx stats skewness and numx stats kurtosis following the same pattern as numx stats variance.
Tech stack
c
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
CGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60