AdaBoost::resample() - Code Metrics - Inspection of "AdaBoost improvements (#53)" - php-ai/php-ml - Measure and Improve Code Quality continuously with Scrutinizer

Test Failed

Push — master ( e8c600...c028a7 )

by Arkadiusz

created 2017-02-28 20:45 UTC

AdaBoost::resample() B

↳ Parent: AdaBoost

Complexity

Conditions	4
Paths	4

Size

Total Lines	23
Code Lines	16

Duplication

Lines	7
Ratio	30.43 %

Importance

Changes

Metric	Value
dl	7
loc	23
rs	8.7972
c	0
b	0
f	0
cc	4
eloc	16
nc	4
nop	0

<?php

declare(strict_types=1);

namespace Phpml\Classification\Ensemble;

use Phpml\Classification\Linear\DecisionStump;
use Phpml\Classification\WeightedClassifier;
use Phpml\Math\Statistic\Mean;
use Phpml\Math\Statistic\StandardDeviation;
use Phpml\Classification\Classifier;
use Phpml\Helper\Predictable;
use Phpml\Helper\Trainable;

class AdaBoost implements Classifier
{
    use Predictable, Trainable;

    /**
     * Actual labels given in the targets array
     * @var array
     */
    protected $labels = [];

    /**
     * @var int
     */
    protected $sampleCount;

    /**
     * @var int
     */
    protected $featureCount;

    /**
     * Number of maximum iterations to be done
     *
     * @var int
     */
    protected $maxIterations;

    /**
     * Sample weights
     *
     * @var array
     */
    protected $weights = [];

    /**
     * List of selected 'weak' classifiers
     *
     * @var array
     */
    protected $classifiers = [];

    /**
     * Base classifier weights
     *
     * @var array
     */
    protected $alpha = [];

    /**
     * @var string
     */
    protected $baseClassifier = DecisionStump::class;

    /**
     * @var array
     */
    protected $classifierOptions = [];

    /**
     * ADAptive BOOSTing (AdaBoost) is an ensemble algorithm to
     * improve classification performance of 'weak' classifiers such as
     * DecisionStump (default base classifier of AdaBoost).
     *
     */
    public function __construct(int $maxIterations = 50)
    {
        $this->maxIterations = $maxIterations;
    }

    /**
     * Sets the base classifier that will be used for boosting (default = DecisionStump)
     *
     * @param string $baseClassifier
     * @param array $classifierOptions
     */
    public function setBaseClassifier(string $baseClassifier = DecisionStump::class, array $classifierOptions = [])
    {
        $this->baseClassifier = $baseClassifier;
        $this->classifierOptions = $classifierOptions;
    }

    /**
     * @param array $samples
     * @param array $targets
     */
    public function train(array $samples, array $targets)
    {
        // Initialize usual variables
        $this->labels = array_keys(array_count_values($targets));
        if (count($this->labels) != 2) {
            throw new \Exception("AdaBoost is a binary classifier and can classify between two classes only");
        }

        // Set all target values to either -1 or 1
        $this->labels = [1 => $this->labels[0], -1 => $this->labels[1]];
        foreach ($targets as $target) {

            $this->targets[] = $target == $this->labels[1] ? 1 : -1;
        }

        $this->samples = array_merge($this->samples, $samples);
        $this->featureCount = count($samples[0]);
        $this->sampleCount = count($this->samples);

        // Initialize AdaBoost parameters
        $this->weights = array_fill(0, $this->sampleCount, 1.0 / $this->sampleCount);
        $this->classifiers = [];
        $this->alpha = [];

        // Execute the algorithm for a maximum number of iterations
        $currIter = 0;
        while ($this->maxIterations > $currIter++) {

            // Determine the best 'weak' classifier based on current weights
            $classifier = $this->getBestClassifier();
            $errorRate = $this->evaluateClassifier($classifier);

            // Update alpha & weight values at each iteration
            $alpha = $this->calculateAlpha($errorRate);
            $this->updateWeights($classifier, $alpha);

            $this->classifiers[] = $classifier;
            $this->alpha[] = $alpha;
        }
    }

    /**
     * Returns the classifier with the lowest error rate with the
     * consideration of current sample weights
     *
     * @return Classifier
     */
    protected function getBestClassifier()
    {
        $ref = new \ReflectionClass($this->baseClassifier);
        if ($this->classifierOptions) {

            $classifier = $ref->newInstanceArgs($this->classifierOptions);
        } else {
            $classifier = $ref->newInstance();
        }

        if (is_subclass_of($classifier, WeightedClassifier::class)) {

            $classifier->setSampleWeights($this->weights);
            $classifier->train($this->samples, $this->targets);
        } else {
            list($samples, $targets) = $this->resample();
            $classifier->train($samples, $targets);
        }

        return $classifier;
    }

    /**
     * Resamples the dataset in accordance with the weights and
     * returns the new dataset
     *
     * @return array
     */
    protected function resample()
    {
        $weights = $this->weights;
        $std = StandardDeviation::population($weights);
        $mean= Mean::arithmetic($weights);
        $min = min($weights);
        $minZ= (int)round(($min - $mean) / $std);

        $samples = [];
        $targets = [];
        foreach ($weights as $index => $weight) {
            $z = (int)round(($weight - $mean) / $std) - $minZ + 1;
            for ($i=0; $i < $z; $i++) {

                if (rand(0, 1) == 0) {
                    continue;
                }
                $samples[] = $this->samples[$index];
                $targets[] = $this->targets[$index];
            }
        }

        return [$samples, $targets];
    }

    /**
     * Evaluates the classifier and returns the classification error rate
     *
     * @param Classifier $classifier
     */
    protected function evaluateClassifier(Classifier $classifier)
    {
        $total = (float) array_sum($this->weights);
        $wrong = 0;
        foreach ($this->samples as $index => $sample) {
            $predicted = $classifier->predict($sample);
            if ($predicted != $this->targets[$index]) {
                $wrong += $this->weights[$index];
            }
        }

        return $wrong / $total;
    }

    /**
     * Calculates alpha of a classifier
     *
     * @param float $errorRate
     * @return float
     */
    protected function calculateAlpha(float $errorRate)
    {
        if ($errorRate == 0) {
            $errorRate = 1e-10;
        }
        return 0.5 * log((1 - $errorRate) / $errorRate);
    }

    /**
     * Updates the sample weights
     *
     * @param Classifier $classifier
     * @param float $alpha
     */
    protected function updateWeights(Classifier $classifier, float $alpha)
    {
        $sumOfWeights = array_sum($this->weights);
        $weightsT1 = [];
        foreach ($this->weights as $index => $weight) {
            $desired = $this->targets[$index];
            $output = $classifier->predict($this->samples[$index]);

            $weight *= exp(-$alpha * $desired * $output) / $sumOfWeights;

            $weightsT1[] = $weight;
        }

        $this->weights = $weightsT1;
    }

    /**
     * @param array $sample
     * @return mixed
     */
    public function predictSample(array $sample)
    {
        $sum = 0;
        foreach ($this->alpha as $index => $alpha) {
            $h = $this->classifiers[$index]->predict($sample);
            $sum += $h * $alpha;
        }

        return $this->labels[ $sum > 0 ? 1 : -1];
    }
}


1		<?php
2
3		declare(strict_types=1);
4
5		namespace Phpml\Classification\Ensemble;
6
7		use Phpml\Classification\Linear\DecisionStump;
8		use Phpml\Classification\WeightedClassifier;
9		use Phpml\Math\Statistic\Mean;
10		use Phpml\Math\Statistic\StandardDeviation;
11		use Phpml\Classification\Classifier;
12		use Phpml\Helper\Predictable;
13		use Phpml\Helper\Trainable;
14
15		class AdaBoost implements Classifier
16		{
17		use Predictable, Trainable;
18
19		/**
20		* Actual labels given in the targets array
21		* @var array
22		*/
23		protected $labels = [];
24
25		/**
26		* @var int
27		*/
28		protected $sampleCount;
29
30		/**
31		* @var int
32		*/
33		protected $featureCount;
34
35		/**
36		* Number of maximum iterations to be done
37		*
38		* @var int
39		*/
40		protected $maxIterations;
41
42		/**
43		* Sample weights
44		*
45		* @var array
46		*/
47		protected $weights = [];
48
49		/**
50		* List of selected 'weak' classifiers
51		*
52		* @var array
53		*/
54		protected $classifiers = [];
55
56		/**
57		* Base classifier weights
58		*
59		* @var array
60		*/
61		protected $alpha = [];
62
63		/**
64		* @var string
65		*/
66		protected $baseClassifier = DecisionStump::class;
67
68		/**
69		* @var array
70		*/
71		protected $classifierOptions = [];
72
73		/**
74		* ADAptive BOOSTing (AdaBoost) is an ensemble algorithm to
75		* improve classification performance of 'weak' classifiers such as
76		* DecisionStump (default base classifier of AdaBoost).
77		*
78		*/
79		public function __construct(int $maxIterations = 50)
80		{
81		$this->maxIterations = $maxIterations;
82		}
83
84		/**
85		* Sets the base classifier that will be used for boosting (default = DecisionStump)
86		*
87		* @param string $baseClassifier
88		* @param array $classifierOptions
89		*/
90		public function setBaseClassifier(string $baseClassifier = DecisionStump::class, array $classifierOptions = [])
91		{
92		$this->baseClassifier = $baseClassifier;
93		$this->classifierOptions = $classifierOptions;
94		}
95
96		/**
97		* @param array $samples
98		* @param array $targets
99		*/
100		public function train(array $samples, array $targets)
101		{
102		// Initialize usual variables
103		$this->labels = array_keys(array_count_values($targets));
104		if (count($this->labels) != 2) {
105		throw new \Exception("AdaBoost is a binary classifier and can classify between two classes only");
106		}
107
108		// Set all target values to either -1 or 1
109		$this->labels = [1 => $this->labels[0], -1 => $this->labels[1]];
110	View Code Duplication	foreach ($targets as $target) {
		0 ignored issues – show Duplication introduced 2017-02-19 10:47 UTC by Report Bug Copy Issue Report This code seems to be duplicated across your project. Duplicated code is one of the most pungent code smells. If you need to duplicate the same code in three or more different places, we strongly encourage you to look into extracting the code into a single class or operation. You can also find more detailed suggestions in the “Code” section of your repository. Loading history...
111		$this->targets[] = $target == $this->labels[1] ? 1 : -1;
112		}
113
114		$this->samples = array_merge($this->samples, $samples);
115		$this->featureCount = count($samples[0]);
116		$this->sampleCount = count($this->samples);
117
118		// Initialize AdaBoost parameters
119		$this->weights = array_fill(0, $this->sampleCount, 1.0 / $this->sampleCount);
120		$this->classifiers = [];
121		$this->alpha = [];
122
123		// Execute the algorithm for a maximum number of iterations
124		$currIter = 0;
125		while ($this->maxIterations > $currIter++) {
126
127		// Determine the best 'weak' classifier based on current weights
128		$classifier = $this->getBestClassifier();
129		$errorRate = $this->evaluateClassifier($classifier);
130
131		// Update alpha & weight values at each iteration
132		$alpha = $this->calculateAlpha($errorRate);
133		$this->updateWeights($classifier, $alpha);
134
135		$this->classifiers[] = $classifier;
136		$this->alpha[] = $alpha;
137		}
138		}
139
140		/**
141		* Returns the classifier with the lowest error rate with the
142		* consideration of current sample weights
143		*
144		* @return Classifier
145		*/
146		protected function getBestClassifier()
147		{
148		$ref = new \ReflectionClass($this->baseClassifier);
149		if ($this->classifierOptions) {
		0 ignored issues – show Bug Best Practice introduced 2017-02-25 14:37 UTC by Report Bug Copy Issue Report The expression `$this->classifierOptions` of type `array` is implicitly converted to a boolean; are you sure this is intended? If so, consider using `! empty($expr)` instead to make it clear that you intend to check for an array without elements. This check marks implicit conversions of arrays to boolean values in a comparison. While in PHP an empty array is considered to be equal (but not identical) to false, this is not always apparent. Consider making the comparison explicit by using `empty(..)` or `! empty(...)` instead. Loading history...
150		$classifier = $ref->newInstanceArgs($this->classifierOptions);
151		} else {
152		$classifier = $ref->newInstance();
153		}
154
155		if (is_subclass_of($classifier, WeightedClassifier::class)) {
		0 ignored issues – show Bug introduced 2017-02-25 14:37 UTC by Report Bug Copy Issue Report Due to PHP Bug #53727, `is_subclass_of` might return inconsistent results on some PHP versions if `\Phpml\Classification\WeightedClassifier::class` can be an interface. If so, you could instead use `ReflectionClass::implementsInterface`. Loading history...
156		$classifier->setSampleWeights($this->weights);
157		$classifier->train($this->samples, $this->targets);
158		} else {
159		list($samples, $targets) = $this->resample();
160		$classifier->train($samples, $targets);
161		}
162
163		return $classifier;
164		}
165
166		/**
167		* Resamples the dataset in accordance with the weights and
168		* returns the new dataset
169		*
170		* @return array
171		*/
172		protected function resample()
173		{
174		$weights = $this->weights;
175		$std = StandardDeviation::population($weights);
176		$mean= Mean::arithmetic($weights);
177		$min = min($weights);
178		$minZ= (int)round(($min - $mean) / $std);
179
180		$samples = [];
181		$targets = [];
182		foreach ($weights as $index => $weight) {
183		$z = (int)round(($weight - $mean) / $std) - $minZ + 1;
184	View Code Duplication	for ($i=0; $i < $z; $i++) {
		0 ignored issues – show Duplication introduced 2017-02-25 14:37 UTC by Report Bug Copy Issue Report This code seems to be duplicated across your project. Duplicated code is one of the most pungent code smells. If you need to duplicate the same code in three or more different places, we strongly encourage you to look into extracting the code into a single class or operation. You can also find more detailed suggestions in the “Code” section of your repository. Loading history...
185		if (rand(0, 1) == 0) {
186		continue;
187		}
188		$samples[] = $this->samples[$index];
189		$targets[] = $this->targets[$index];
190		}
191		}
192
193		return [$samples, $targets];
194		}
195
196		/**
197		* Evaluates the classifier and returns the classification error rate
198		*
199		* @param Classifier $classifier
200		*/
201		protected function evaluateClassifier(Classifier $classifier)
202		{
203		$total = (float) array_sum($this->weights);
204		$wrong = 0;
205		foreach ($this->samples as $index => $sample) {
206		$predicted = $classifier->predict($sample);
207		if ($predicted != $this->targets[$index]) {
208		$wrong += $this->weights[$index];
209		}
210		}
211
212		return $wrong / $total;
213		}
214
215		/**
216		* Calculates alpha of a classifier
217		*
218		* @param float $errorRate
219		* @return float
220		*/
221		protected function calculateAlpha(float $errorRate)
222		{
223		if ($errorRate == 0) {
224		$errorRate = 1e-10;
225		}
226		return 0.5 * log((1 - $errorRate) / $errorRate);
227		}
228
229		/**
230		* Updates the sample weights
231		*
232		* @param Classifier $classifier
233		* @param float $alpha
234		*/
235		protected function updateWeights(Classifier $classifier, float $alpha)
236		{
237		$sumOfWeights = array_sum($this->weights);
238		$weightsT1 = [];
239		foreach ($this->weights as $index => $weight) {
240		$desired = $this->targets[$index];
241		$output = $classifier->predict($this->samples[$index]);
242
243		$weight = exp(-$alpha $desired * $output) / $sumOfWeights;
244
245		$weightsT1[] = $weight;
246		}
247
248		$this->weights = $weightsT1;
249		}
250
251		/**
252		* @param array $sample
253		* @return mixed
254		*/
255		public function predictSample(array $sample)
256		{
257		$sum = 0;
258		foreach ($this->alpha as $index => $alpha) {
259		$h = $this->classifiers[$index]->predict($sample);
260		$sum += $h * $alpha;
261		}
262
263		return $this->labels[ $sum > 0 ? 1 : -1];
264		}
265		}
266

php-ai / php-ml

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AdaBoost::resample() B

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