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weighted_percentile should error/warn when all sample weights 0 #31032

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lucyleeow opened this issue Mar 20, 2025 · 1 comment
Open

weighted_percentile should error/warn when all sample weights 0 #31032

lucyleeow opened this issue Mar 20, 2025 · 1 comment
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@lucyleeow
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Describe the bug

Noticed while working on #29431

Steps/Code to Reproduce

See the following test:

scikit-learn/sklearn/utils/tests/test_stats.py

Lines 67 to 73 in cd0478f

def test_weighted_percentile_zero_weight():
y = np.empty(102, dtype=np.float64)
y.fill(1.0)
sw = np.ones(102, dtype=np.float64)
sw.fill(0.0)
value = _weighted_percentile(y, sw, 50)
assert approx(value) == 1.0

Expected Results

Error or warning should probably be given. You're effectively asking for a quantile of a empty array.

Actual Results

When all sample weights are 0, what happens is that percentile_in_sorted (as in the index of desired observation in array is the) is 101 (the last item). We should probably add a check and give a warning when sample_weights is all zero

cc @ogrisel @glemaitre

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@lucyleeow lucyleeow added Bug Needs Triage Issue requires triage labels Mar 20, 2025
@DanieSimonlLowe DanieSimonlLowe mentioned this issue Mar 20, 2025
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@adrinjalali
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cc @antoinebaker too on this one.

@adrinjalali adrinjalali removed the Needs Triage Issue requires triage label Mar 21, 2025
@lucyleeow lucyleeow mentioned this issue Mar 26, 2025
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@adrinjalali @lucyleeow