[rtmalikian]

Fixes #9220.

Description

partition_dataset rounded each partition's size independently (int(r / rsum * data_len + 0.5)), so the rounded sizes could sum to less than len(data) and trailing items ended up in no partition — e.g. ratios [1, 1, 1] on 10 items gave [[0, 1, 2], [3, 4, 5], [6, 7, 8]] (item 9 lost), and [0.8, 0.1, 0.1] on 63 items gave sizes [50, 6, 6] (one case lost). The fix computes the rounded sizes first and, only when they fall short of data_len, assigns the remainder to the last partition, so every item lands in exactly one partition. All other behaviour is unchanged: the docstring example ([0.6, 0.2, 0.2] on 5 items) and the overshoot case (capped at data_len) behave exactly as before. partition_dataset_classes benefits automatically since it delegates to this function.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running the partition dataset unit tests (see Verification).
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

Verification

• PYTHONPATH=. python -m pytest tests/data/test_partition_dataset.py tests/data/test_partition_dataset_classes.py -q: 16 passed (12 partition cases incl. 4 new, 4 classes cases).
• Negative control (fix stashed, new tests kept): exactly the 3 new loss-case tests fail; all 9 pre-existing partition tests pass.
• Issue repro post-fix: [0.8, 0.1, 0.1] on 63 items (shuffled, seed 0) gives sizes [50, 6, 7] with zero lost items; [1, 1, 1] on 10 items gives [[0, 1, 2], [3, 4, 5], [6, 7, 8, 9]].
• Exhaustive sweep post-fix: for ratios [0.8, 0.1, 0.1], [1, 1, 1], and [1, 1, 1, 1, 1], every length from 1 to 1000 partitions with no lost or duplicated items.
• ruff check clean on both touched files; ruff format --check clean.

Additional Notes

Author

Raphael Malikian, rtmalikian@gmail.com — If you'd like similar help with your own project or codebase, I'm open to collaborate — feel free to reach out.
This PR was prepared with AI assistance.

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Walkthrough

The ratio-based branch of partition_dataset now adds any items left after rounded partition sizes to the last partition. New test cases cover equal and fractional ratios across several dataset lengths.

Priority: Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Severity of issue fixed: Medium

Merge Risk: Low · up to afff1

The fix retains items that were previously lost. A zero-ratio final partition can receive a remainder item, but whether that conflicts with intended behavior is unconfirmed; the PR is mergeable with owner awareness.

Pre-merge checks: 5

Check name	Status	Explanation
Title check		The title names the main change: partition_dataset no longer drops items when rounded ratio sizes sum to less than the dataset length. It matches the raw summary, which says the remainder goes to the …
Description check		The description follows the template. It has the Fixes line (#9220), a Description section explaining the rounding bug and fix, and the Types of changes checklist with the applicable items marked. It …
Linked Issues check		Issue #9220 requires every item to appear in exactly one ratio-based partition. The reviewed change computes all rounded sizes first and adds any shortfall to the last partition. Existing slicing stil…
Out of Scope Changes check		The reported changes are limited to the ratio-size calculation in monai/data/utils.py and focused partition_dataset tests. These changes directly implement and verify issue #9220. No unrelated cha…
Docstring Coverage		Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Documentation-only edits and deletions within survi…

Full details: Title check

Explanation

The title names the main change: partition_dataset no longer drops items when rounded ratio sizes sum to less than the dataset length. It matches the raw summary, which says the remainder goes to the last partition.

Full details: Description check

Explanation

The description follows the template. It has the Fixes line (#9220), a Description section explaining the rounding bug and fix, and the Types of changes checklist with the applicable items marked. It also adds Verification and Additional Notes sections. The in-line docstrings and documentation items are unchecked, which is acceptable because the change does not alter the docstring.

Full details: Linked Issues check

Explanation

Issue #9220 requires every item to appear in exactly one ratio-based partition. The reviewed change computes all rounded sizes first and adds any shortfall to the last partition. Existing slicing still caps overshoot at data_len. Tests cover the reported 3-way, fractional, 5-way, and documented cases. partition_dataset_classes delegates to this function and therefore receives the fix.

Full details: Out of Scope Changes check

Explanation

The reported changes are limited to the ratio-size calculation in monai/data/utils.py and focused partition_dataset tests. These changes directly implement and verify issue #9220. No unrelated change is shown.

Full details: Docstring Coverage

Explanation

Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 1 functions across 2 files.

Finishing Touches

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🔇 Additional comments: 1

monai/data/utils.py-1212-1212: 1

1212-1212: Minor · Functional Correctness · Quick win

⚠️ Unverified finding
Verification ran but could not confirm this finding. It is shown for review, not as a verified issue.

Keep zero-ratio partitions empty.

With 10 items and ratios [1, 1, 1, 0], sizes is [3, 3, 3, 0]. This line assigns the remaining item to the zero-ratio partition. Add the shortfall to the last partition with a positive ratio, and test this case. (raw.githubusercontent.com)

As per path instructions, “Examine code for logical error or inconsistencies, and suggest what may be changed to addressed these.”

Source: Path instructions

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Review info

Run configuration

• Source mode: Auto
• Repository: Project-MONAI/MONAI
• Branch: dev
• File: .coderabbit.yaml
• Commit: e0cee14
• Layers: Repository YAML
• Review profile: CHILL
• Plan: Advanced
• Run ID: f8b38bb3-6ea5-44ca-8642-82e1304678f7

Commits

Reviewing files that changed from the base of the PR and between e0cee14 and afff1e3.

Files selected for processing: 2

• monai/data/utils.py
• tests/data/test_partition_dataset.py

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