#2331 made Precision and F1Score include classes that appear only in
predictions, and added regression tests to both. Recall was not touched, so
the line #2331 replaced is still there and the three metrics disagree about
which classes exist for identical input:
precision.matched_classes -> [0 1] precision_per_class (2, 10)
recall.matched_classes -> [0] recall_per_class (1, 10)
f1.matched_classes -> [0 1]
These read as parallel outputs, so zipping them silently truncates rather
than raising.
Recall for a class with no ground-truth instances is 0.0 rather than
undefined, which is what sklearn reports (it infers labels from the union of
y_true and y_pred) and what #2331 cited as its own standard. MICRO is
unchanged because an absent class contributes no false negatives, and
WEIGHTED is unchanged because its ground-truth support is zero. MACRO does
change, and the changelog says so.
Also of note: recall.py already carried #2331's WEIGHTED zero-support guard,
whose comment refers to 'only false-positive classes'. That state could not
arise in recall.py, because unique_classes came from ground truth alone. The
guard was propagated; the union that gives it meaning was not.
Addresses the review on #2468. Building the class union inside
_compute_recall_for_classes only covers samples that reach it, and samples with
predictions but no targets are skipped earlier in _compute. So matched_classes
could still disagree with Precision and F1Score for list inputs containing a
background image, which is the exact invariant the new test asserts.
Before, for one normal sample plus one background image predicting class 2:
precision.matched_classes -> [0 2]
recall.matched_classes -> [0]
Recall now handles len(targets) == 0 and len(predictions) > 0 the way Precision
does. No recall value changes, since a background image produces no false
negatives; only the tracked class set does.
* test: cover Recall bg-image size-bucket, dup & non-contiguous ids
* docs: strengthen Recall changelog migration note
* docs+perf: Recall doctest example; dedupe-then-union micro-opt
---------
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Jirka Borovec <6035284+Borda@users.noreply.github.com>
Co-authored-by: claude[bot] <209825114+claude[bot]@users.noreply.github.com>
Co-authored-by: OpenAI Codex <codex@openai.com>
7fc91180fe