FA-14205 / Numerical aggregation / Member archive

Group balanced squared loss: Within-group loss totals are not normalized by group sizes. · case 05

The reduction disagrees with its explicit aggregation oracle.

Member previewVariant 5 · 3 implementations · 9 checks per implementation

Case contract

Rows [group label, integer residual or None] are reduced into mean squared residual per group, then arithmetic mean across observed groups. Missing residuals contribute neither count nor group presence; group labels are case-sensitive. Empty observed population returns None. Exact Fraction string.

Why this case matters

Exact bounded examples isolate a reduction defect without floating-point or external-service effects.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression 1	`"21/2"`	`"37/4"`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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