Improve distance performance and reduce duplication in distance classes. (#348)

* Issue #347: Reduce duplicated code.

* Issue #347: Replace array_* with regular loops for better perfomance.

src/Math/Distance/Chebyshev.php

@@ -4,27 +4,16 @@ declare(strict_types=1);
 
 namespace Phpml\Math\Distance;
 
-use Phpml\Exception\InvalidArgumentException;
-use Phpml\Math\Distance;
-
-class Chebyshev implements Distance
+/**
+ * Class Chebyshev
+ */
+class Chebyshev extends Distance
 {
     /**
-     * @throws InvalidArgumentException
+     * {@inheritdoc}
      */
     public function distance(array $a, array $b): float
     {
-        if (count($a) !== count($b)) {
-            throw new InvalidArgumentException('Size of given arrays does not match');
-        }
-
-        $differences = [];
-        $count = count($a);
-
-        for ($i = 0; $i < $count; ++$i) {
-            $differences[] = abs($a[$i] - $b[$i]);
-        }
-
-        return max($differences);
+        return max($this->deltas($a, $b));
     }
 }

src/Math/Distance/Distance.php

+<?php
+
+declare(strict_types=1);
+
+namespace Phpml\Math\Distance;
+
+use Phpml\Exception\InvalidArgumentException;
+use Phpml\Math\Distance as DistanceInterface;
+
+/**
+ * Class Distance
+ */
+abstract class Distance implements DistanceInterface
+{
+    /**
+     * @var float|int
+     */
+    public $norm;
+
+    /**
+     * Distance constructor.
+     */
+    public function __construct(float $norm = 3.0)
+    {
+        $this->norm = $norm;
+    }
+
+    /**
+     * @throws InvalidArgumentException
+     */
+    public function distance(array $a, array $b): float
+    {
+        $distance = 0;
+
+        foreach ($this->deltas($a, $b) as $delta) {
+            $distance += $delta ** $this->norm;
+        }
+
+        return $distance ** (1 / $this->norm);
+    }
+
+    /**
+     * @throws InvalidArgumentException
+     */
+    protected function deltas(array $a, array $b): array
+    {
+        $count = count($a);
+
+        if ($count !== count($b)) {
+            throw new InvalidArgumentException('Size of given arrays does not match');
+        }
+
+        $deltas = [];
+
+        for ($i = 0; $i < $count; $i++) {
+            $deltas[] = abs($a[$i] - $b[$i]);
+        }
+
+        return $deltas;
+    }
+}

src/Math/Distance/Euclidean.php

@@ -4,31 +4,25 @@ declare(strict_types=1);
 
 namespace Phpml\Math\Distance;
 
-use Phpml\Exception\InvalidArgumentException;
-use Phpml\Math\Distance;
-
-class Euclidean implements Distance
+/**
+ * Class Euclidean
+ *
+ * L^2 Metric.
+ */
+class Euclidean extends Distance
 {
     /**
-     * @throws InvalidArgumentException
+     * Euclidean constructor.
      */
-    public function distance(array $a, array $b): float
+    public function __construct()
     {
-        if (count($a) !== count($b)) {
-            throw new InvalidArgumentException('Size of given arrays does not match');
-        }
-
-        $distance = 0;
-
-        foreach ($a as $i => $val) {
-            $distance += ($val - $b[$i]) ** 2;
-        }
-
-        return sqrt((float) $distance);
+        parent::__construct(2.0);
     }
 
     /**
      * Square of Euclidean distance
+     *
+     * @throws \Phpml\Exception\InvalidArgumentException
      */
     public function sqDistance(array $a, array $b): float
     {

src/Math/Distance/Manhattan.php

@@ -4,22 +4,18 @@ declare(strict_types=1);
 
 namespace Phpml\Math\Distance;
 
-use Phpml\Exception\InvalidArgumentException;
-use Phpml\Math\Distance;
-
-class Manhattan implements Distance
+/**
+ * Class Manhattan
+ *
+ * L^1 Metric.
+ */
+class Manhattan extends Distance
 {
     /**
-     * @throws InvalidArgumentException
+     * Manhattan constructor.
      */
-    public function distance(array $a, array $b): float
+    public function __construct()
     {
-        if (count($a) !== count($b)) {
-            throw new InvalidArgumentException('Size of given arrays does not match');
-        }
-
-        return array_sum(array_map(function ($m, $n) {
-            return abs($m - $n);
-        }, $a, $b));
+        parent::__construct(1.0);
     }
 }

src/Math/Distance/Minkowski.php

@@ -4,37 +4,11 @@ declare(strict_types=1);
 
 namespace Phpml\Math\Distance;
 
-use Phpml\Exception\InvalidArgumentException;
-use Phpml\Math\Distance;
-
-class Minkowski implements Distance
+/**
+ * Class Minkowski
+ *
+ * L^n Metric.
+ */
+class Minkowski extends Distance
 {
-    /**
-     * @var float
-     */
-    private $lambda;
-
-    public function __construct(float $lambda = 3.0)
-    {
-        $this->lambda = $lambda;
-    }
-
-    /**
-     * @throws InvalidArgumentException
-     */
-    public function distance(array $a, array $b): float
-    {
-        if (count($a) !== count($b)) {
-            throw new InvalidArgumentException('Size of given arrays does not match');
-        }
-
-        $distance = 0;
-        $count = count($a);
-
-        for ($i = 0; $i < $count; ++$i) {
-            $distance += pow(abs($a[$i] - $b[$i]), $this->lambda);
-        }
-
-        return (float) pow($distance, 1 / $this->lambda);
-    }
 }