Refactor SpearmanRankCorrelation to native PyTorch and remove SciPy dependency

[Prathamesh8989]

Fixes #3663

Description

This PR refactors the SpearmanRankCorrelation metric to use native PyTorch operations, effectively removing the hard dependency on scipy for calculation.

Key Changes:

• Native Ranking Implementation: Added a _get_ranks helper function that calculates ranks using the "average" method for ties, ensuring parity with scipy.stats.spearmanr.
• Logic Update: Replaced the SciPy-based _spearman_r function with a pure PyTorch implementation using Pearson correlation on ranked tensors.
• Robust Testing: Updated the test suite to treat SciPy as an optional "gold standard" check. If SciPy is missing, tests skip gracefully instead of crashing, but the metric remains fully functional.
• Improved Performance: By keeping operations in PyTorch, we reduce unnecessary CPU/GPU synchronization and data transfers.

Check list:

• New tests are added (Updated existing tests to handle optional dependency)
• New doc strings: description and/or example code are in RST format
• Documentation is updated (Updated "Implementation" section in docstrings)

[Prathamesh8989]

Hi @TahaZahid05,

Thank you for the feedback!

I've addressed the suggested changes and updated the implementation accordingly. Please let me know if there are any further adjustments needed from my side.

[Prathamesh8989]

Hi @TahaZahid05,

Thanks for the suggestions!

I've made the requested updates:

Switched the rank calculation to use .double() for improved numerical stability.
Added tests to ensure the metric returns NaN when inputs contain NaN values.
Added a test for constant inputs.
Added a test verifying the average rank calculation using [10, 20, 20, 30].

Please let me know if any further adjustments are needed.

[TahaZahid05]

Just one last change, else everything else is good!

[Prathamesh8989]

@TahaZahid05,
Thanks for the suggestion! I've added the versionchanged:: 0.5.5 entry in the docstring to document the switch to the native PyTorch implementation and removal of the SciPy dependency.

Please let me know if anything else needs adjustment.

[TahaZahid05]

Thanks for the changes @Prathamesh8989. @vfdev-5 Looks good to me!

[TahaZahid05]

@Prathamesh8989, style checks are failing. Kindly fix them.

[Prathamesh8989]

yeah sure , fixing them.

[vfdev-5]

Why do we add packaging here?
We already have it as ignite depedency here:

ignite/pyproject.toml

Line 20 in 6c3dfd9

"packaging"

[Prathamesh8989]

it gave me an error saying that the tests failed because of not having this , so tried to add this in requirements.txt

[vfdev-5]

Let's remove it

[TahaZahid05]

@Prathamesh8989 can you please verify your pre-commit installation? The code style checks are still failing. You may take a look at CONTRIBUTING.MD for more reference.

[Prathamesh8989]

sure, i will get through it by tomorrow.

[TahaZahid05]

@Prathamesh8989 it seems you have pushed unwanted changes when fixing the code style checks. All files in examples are also coming under file changed. Can you fix it?

[Prathamesh8989]

Hey @TahaZahid05,

I ran pre-commit run --all-files, then staged, committed, and pushed the files. I believe that should be the correct workflow, but I might be missing something. Could you please guide me a bit on this? I haven’t yet figured out the proper way to verify it.

Also, I’ll be having my practical and theory exams from 22nd to 30th April, so my response time might be a bit slow during that period. Kindly excuse the delay in advance.

[TahaZahid05]

@Prathamesh8989 Run the following set of commands:

pip install -U pre-commit 
pre-commit clean           
pre-commit install         
pre-commit run --all-files 

You'll see in your terminal:

nb-clean.................................................................Passed
check toml...............................................................Passed
check yaml...............................................................Passed
fix end of files.........................................................Passed
trim trailing whitespace.................................................Passed
prettier.................................................................Passed
ruff check...............................................................Passed
ruff format..............................................................Failed
- hook id: ruff-format
- files were modified by this hook

1 file reformatted, 364 files left unchanged

Then run git add . again to stage the change pre-commit made, and then commit and push. Follow along these steps and let me know where your output is deviating or if you get stuck somewhere, I can help you out from there. You can contact me on Discord if you need further help

[vfdev-5]

@Prathamesh8989 the failure on MPS is real: https://github.com/pytorch/ignite/actions/runs/24736092143/job/72390524588?pr=3672
MPS does not have f64.