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ENH Warn in SelectKBest when k > n_features #27841

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Merged
lorentzenchr merged 5 commits into from
Dec 1, 2023
Merged

ENH Warn in SelectKBest when k > n_features #27841

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2b57d5b
API Warn in SelectKBest when k > n_features
thomasjpfan Nov 24, 2023
f946f3e
DOC Adds whats new
thomasjpfan Nov 24, 2023
303802f
Apply suggestions from code review
thomasjpfan Nov 25, 2023
285828f
Merge remote-tracking branch 'upstream/main' into select_k_best_warning
thomasjpfan Dec 1, 2023
efb6f2a
DOC Update to enhacement
thomasjpfan Dec 1, 2023
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5 changes: 5 additions & 0 deletions doc/whats_new/v1.4.rst
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Expand Up @@ -374,6 +374,11 @@ Changelog
not check for nans during input validation.
:pr:`21807` by `Thomas Fan`_.

- |Enhancement| :class:`feature_selection.SelectKBest` and
:class:`feature_selection.GenericUnivariateSelect` with `mode='k_best'`
now shows a warning when `k` is greater than the number of features.
:pr:`27841` by `Thomas Fan`_.

:mod:`sklearn.inspection`
.........................

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6 changes: 3 additions & 3 deletions sklearn/feature_selection/_univariate_selection.py
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Expand Up @@ -703,9 +703,9 @@ def __init__(self, score_func=f_classif, *, k=10):

def _check_params(self, X, y):
if not isinstance(self.k, str) and self.k > X.shape[1]:
raise ValueError(
f"k should be <= n_features = {X.shape[1]}; "
f"got {self.k}. Use k='all' to return all features."
warnings.warn(
f"k={self.k} is greater than n_features={X.shape[1]}. "
"All the features will be returned."
)

def _get_support_mask(self):
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5 changes: 3 additions & 2 deletions sklearn/feature_selection/tests/test_feature_select.py
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Expand Up @@ -831,9 +831,10 @@ def test_invalid_k():
X = [[0, 1, 0], [0, -1, -1], [0, 0.5, 0.5]]
y = [1, 0, 1]

with pytest.raises(ValueError):
msg = "k=4 is greater than n_features=3. All the features will be returned."
with pytest.warns(UserWarning, match=msg):
SelectKBest(k=4).fit(X, y)
with pytest.raises(ValueError):
with pytest.warns(UserWarning, match=msg):
GenericUnivariateSelect(mode="k_best", param=4).fit(X, y)


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