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Correct SVM Use #346

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merged 3 commits into from
Nov 2, 2024
Merged

Correct SVM Use #346

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c3897a3
Correct SVM Use
LouisAUTHIE Oct 29, 2024
011b52f
Update OneClassSVM.php
LouisAUTHIE Oct 30, 2024
851df84
Update OneClassSVM.php
LouisAUTHIE Nov 1, 2024
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18 changes: 16 additions & 2 deletions src/AnomalyDetectors/OneClassSVM.php
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Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,7 @@ public function __construct(
new ExtensionIsLoaded('svm'),
new ExtensionMinimumVersion('svm', '0.2.0'),
])->check();


if ($nu < 0.0 or $nu > 1.0) {
throw new InvalidArgumentException('Nu must be between'
Expand Down Expand Up @@ -182,7 +183,14 @@ public function train(Dataset $dataset) : void
new SamplesAreCompatibleWithEstimator($dataset, $this),
])->check();

$this->model = $this->svm->train($dataset->samples());
$data = [];

foreach ($dataset->samples() as $sample) {
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So did array_unshift() turn out to be faster?

Is it necessary to assign the sample to an intermediate variable or would

foreach ($dataset->samples() as $sample) {
    array_unshift($sample, 1);

    $data[] = $sample;
}

work here as well?

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It is faster yes. And the rest works also, please see the next commit

array_unshift($sample, 1);
$data[] = $sample;
}

$this->model = $this->svm->train($data);
}

/**
Expand Down Expand Up @@ -211,7 +219,13 @@ public function predictSample(array $sample) : int
throw new RuntimeException('Estimator has not been trained.');
}

return $this->model->predict($sample) !== 1.0 ? 0 : 1;
$sampleWithOffset = [];

foreach ($sample as $key => $value) {
$sampleWithOffset[$key + 1] = $value;
}

return $this->model->predict($sampleWithOffset) == 1 ? 0 : 1;
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I notice we are "inversing" the logic here i.e. 1 is now 0, 0 is now 1. Is that intentional?

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Yes, in fact in the one class mode of libsvm, the "normal" samples are to be labelled with the 1 class. And the anomalies, are to be labelled with -1. That's why !

}

/**
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