Disposal

[henrydingliu]

Summary of Changes

Related GitHub Issue(s)

Additional Context for Reviewers

• I passed tests locally for both code (uv run pytest) and documentation changes (uv run jb build docs --builder=custom --custom-builder=doctest)

---

Note

Medium Risk
Removing incr_to_cum on fit changes disposal-rate inputs for non-cumulative triangles, and ultimate/backend alignment in transform can alter forecasts if backends or shapes were previously inconsistent.

Overview
DisposalRate now validates sample_weight (ultimate) against X in both fit and transform via shared MethodBase.validate_weight, matching chainladder methods behavior when shapes may broadcast.

Fit no longer forces incr_to_cum() on the loss triangle before building disposal rates; it keeps a sorted copy as self.X_ and uses that for weights, parent super().fit, and the terminal disposal concat. Transform sets ultimate_ from the ultimate triangle’s latest diagonal on the same array backend as the fitted X_, instead of taking latest_diagonal without backend alignment.

MethodBase.validate_weight is refactored to a @staticmethod with Triangle type hints and a short docstring so DisposalRate can call it without duplicating logic.

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[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

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[cursor]

Sorted X_ mismatches disposal triangle

High Severity

fit stores a sorted triangle in self.X_ but builds disposal_rate_tri from the unsorted local X. Weights and super().fit then mix sorted self.X_.values with rates and ult.values tied to the original row order, so origins can be paired incorrectly whenever the index is not already sorted.

Additional Locations (1)

• chainladder/adjustments/disposal.py#L231-L232

 

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[cursor]

Removed cumulative conversion in fit

Medium Severity

fit no longer calls incr_to_cum() on X after copying or setting the numpy backend. Disposal rates are cumulative paid (or similar) divided by ultimate; fitting on incremental values yields incorrect ratios and regression inputs for incremental triangles.

 

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[codecov]

Codecov Report

❌ Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.24%. Comparing base (d6bbdac) to head (0c1830d).
⚠️ Report is 9 commits behind head on disposal_rate_method.

Files with missing lines	Patch %	Lines
chainladder/adjustments/disposal.py	84.61%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##           disposal_rate_method    #1039      +/-   ##
========================================================
- Coverage                 89.25%   89.24%   -0.02%     
========================================================
  Files                        91       91              
  Lines                      5242     5233       -9     
  Branches                    666      666              
========================================================
- Hits                       4679     4670       -9     
- Misses                      394      396       +2     
+ Partials                    169      167       -2     

Flag	Coverage Δ
unittests	89.24% <88.23%> (-0.02%)	⬇️

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