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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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17 changes: 15 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 +183,13 @@ public function train(Dataset $dataset) : void
new SamplesAreCompatibleWithEstimator($dataset, $this),
])->check();

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

foreach ($dataset->samples() as $i => $sample) {
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Looks like we don't need this $i variable

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You are completely right, this is now corrected !

$data[] = array_merge([1], $sample);
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I wonder which is faster ...

array_merge([1], $sample)

or

array_unshift(1, $sample)

From what I recall, unshift is linear because it needs to reindex the array or something. I think merge is also linear.

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Change is done ;)

}

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

/**
Expand Down Expand Up @@ -211,7 +218,13 @@ 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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