fix(tdigest): preserve stored min and max when merging - #525
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Merging a digest whose extreme centroids have weight greater than one re-derived min and max from those centroid means. Copy the stored extrema from the other digest first so rank and quantile tail interpolation stay correct, especially for deserialized images.
leerho
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Sep 17, 2026
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Summary
min_/max_from the other digest intdigest::mergebefore compressing the combined centroid list.Why
mergepreviously re-derived extrema from the extreme centroid means. That is exact only when those centroids have unit weight. Deserialized images (and the reference implementation format) can have weighted tails, so min/max drifted inward and rank/quantile tail interpolation used the wrong endpoints.Same defect as apache/datasketches-rust#277.
Validation
tdigest_testincludingmerge preserves deserialized min max with weighted tailsand the full[tdigest]suite (49 cases).