Fix MultiIndex error in compute_forward_displacement (#794)

[Tushar7012]

Replace reindex(data.coords) with reindex_like(data) to avoid a RuntimeError when DataArray coordinates originate from pandas MultiIndex levels that carry the _no_setting_name flag.

• Fix _compute_forward_displacement (line 129)
• Fix compute_displacement (line 115, deprecated)
• Add regression test test_forward_displacement_with_multiindex_coords

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Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?

When compute_forward_displacement is called with an xarray DataArray created from a pandas MultiIndex (via to_xarray()), the current implementation fails with a RuntimeError.
This happens because reindex(data.coords) internally attempts to rename index levels, which pandas explicitly disallows for MultiIndex objects with the _no_setting_name flag.

As a result, valid inputs can unexpectedly fail even though the underlying data is correct.

What does this PR do?

This PR replaces the use of reindex(data.coords, fill_value=0) with reindex_like(data, fill_value=0) in both the active and deprecated code paths.

reindex_like() provides the same alignment and fill behavior while avoiding index-level name mutation, making the function safe for MultiIndex-backed inputs. A regression test has also been added to ensure this case remains supported going forward.

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References

• Fixes MultiIndex error with specific inputs to compute_forward_displacement #794

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How has this PR been tested?

• Added a regression test (test_forward_displacement_with_multiindex_coords) based on the reproducible example provided in the issue
• Verified that the test fails on the current main branch and passes with this change
• Ran the full test suite locally to ensure no existing behavior is affected

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Is this a breaking change?

No. This change preserves existing behavior and only affects internal reindexing logic to improve robustness for specific input types.

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Does this PR require an update to the documentation?

No. This is an internal bug fix and does not change the public API or user-facing behavior.

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Checklist

• The code has been tested locally
• Tests have been added to cover the reported issue
• The documentation has been updated to reflect any changes (not required)
• The code has been formatted with pre-commit

[Copilot]

Pull request overview

Fixes a RuntimeError in compute_forward_displacement (and the deprecated compute_displacement) when the input xarray.DataArray originates from a pandas MultiIndex (e.g., via Series.to_xarray()), by switching to reindex_like() to avoid index-level name mutation.

Changes:

• Replace reindex(data.coords) with reindex_like(data) in _compute_forward_displacement.
• Apply the same fix in the deprecated compute_displacement path.
• Add a regression unit test covering MultiIndex-derived coordinate inputs (issue #794).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
movement/kinematics/kinematics.py	Uses reindex_like(data, fill_value=0) to align diff results back to the original array without triggering MultiIndex level-name mutation.
tests/test_unit/test_kinematics/test_kinematics.py	Adds a regression test ensuring compute_forward_displacement works with DataArrays created from a pandas MultiIndex via .to_xarray().

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (ddec403) to head (0d7ddff).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

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##              main      #799   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           36        36           
  Lines         2205      2205           
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  Hits          2205      2205           

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[Tushar7012]

Hey @sfmig ,Thank you for the feedback. I apologize for the accidental inclusion of unrelated documentation changes. I have updated the PR to strictly focus on the MultiIndex bug fix and its accompanying regression test...

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sfmig]

Hi @Tushar7012 thanks for this and apologies for the slow response!
I think this is good to go now, I just rephrased a bit the docstring in the test for clarity.