FA-100383 / Feature preprocessing fit scope / Member archive

Variance selector learns feature support from held-out rows · case 03

The fitted feature projection changes the dimensionality of transformed numeric rows.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

Train and rows are nonempty rectangular numeric matrices with equal width; threshold is nonnegative. Fit population variance per training column and retain columns with variance strictly greater than threshold, preserving original order.

Why this case matters

A fitted column projection demonstrates how training-only statistics control later feature transforms.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
heldout variance ignored	`[[2, 2]]`	`[[2]]`	Failed

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