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@GaetandeCast GaetandeCast commented Sep 22, 2025

Reference Issues/PRs

Fixes #32201

What does this implement/fix? Explain your changes.

To be used in RFE and RFECV, permutation_importance needs to be aware of which features were already eliminated by the procedure to reduce its test dataset.
This PR adds a feature_indices parameter to sklearn.feature_selection._base._get_feature_importances that is given to the importance_getter so that it is aware of which features to compute the importance of.

Any other comments?

The new feature is added to the test suite and illustrated in the RFECV doc example.

@glemaitre @ogrisel

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@GaetandeCast GaetandeCast changed the title base logic and test FEAT allow RFE(CV) be used with pemutation_importance Sep 22, 2025
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Thanks for the PR. This is very useful. Please indeed update the example and add a changelog entry.

EDIT: here are the instructions for the changelog entry: https://github.com/scikit-learn/scikit-learn/blob/main/doc/whats_new/upcoming_changes/README.md

Comment on lines 7 to 8
This allows methods like :func:`permutation_importance` to extract the relevant features
from its test set.
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Suggested change
This allows methods like :func:`permutation_importance` to extract the relevant features
from its test set.
This allows methods like :func:`permutation_importance` and similar tools to
iteratively extract the previously selected features from a test set.

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yeah I realized it was not very clear so I planned to change it to:
" This allows methods that need a test set, like :func:permutation_importance, to know which
features of to use in their predictions."

@GaetandeCast GaetandeCast marked this pull request as ready for review September 25, 2025 14:13
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LGTM besides the following:

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I found a small problem in the example + small suggestions for further improvement in the docstrings.

Also @ArturoAmorQ might be interested in reviewing this PR (the updated example in particular).

If `callable`, overrides the default feature importance getter.
The callable is passed with the fitted estimator and it should
return importance for each feature.
return importance for each feature. When it accepts it, the callable is passed
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Suggested change
return importance for each feature. When it accepts it, the callable is passed
return importance for each feature. When it accepts it, the callable is passed

return importance for each feature.
return importance for each feature. When it accepts it, the callable is passed
`feature_indices` which stores the index of the features in the full dataset
that have not been eliminated yet.
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Suggested change
that have not been eliminated yet.
that have not yet been eliminated in previous iterations.

return importance for each feature.
return importance for each feature. When it accepts it, the callable is passed
`feature_indices` which stores the index of the features in the full dataset
that have not been eliminated yet.
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Suggested change
that have not been eliminated yet.
that have not yet been eliminated in previous iterations.

shown at the end of
:ref:`sphx_glr_auto_examples_feature_selection_plot_rfe_with_cross_validation.py`.
.. versionadded:: 0.24
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I think we should add a .. versionchanged:: 1.8 and mention that support for passing feature_indices to the callable when part of its signature.

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And similarly for the docstring of the other class.

n_classes=8,
n_clusters_per_class=1,
class_sep=0.8,
random_state=0,
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We need to make sure that we do not sample from the training set:

Suggested change
random_state=0,
random_state=1, # Use a different seed to sample different points.

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[FEAT] Let importance_getter from RFE accept test data for permutation importance
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