create imputer tool for completing missing values

src/Phpml/Preprocessing/Imputer.php

@@ -0,0 +1,86 @@
+<?php
+
+declare (strict_types = 1);
+
+namespace Phpml\Preprocessing;
+
+use Phpml\Preprocessing\Imputer\Strategy;
+
+class Imputer implements Preprocessor
+{
+    const AXIS_COLUMN = 0;
+    const AXIS_ROW = 1;
+
+    /**
+     * @var mixed
+     */
+    private $missingValue;
+
+    /**
+     * @var Strategy
+     */
+    private $strategy;
+
+    /**
+     * @var int
+     */
+    private $axis;
+
+    /**
+     * @param mixed    $missingValue
+     * @param Strategy $strategy
+     * @param int      $axis
+     */
+    public function __construct($missingValue = null, Strategy $strategy, int $axis = self::AXIS_COLUMN)
+    {
+        $this->missingValue = $missingValue;
+        $this->strategy = $strategy;
+        $this->axis = $axis;
+    }
+
+    /**
+     * @param array $samples
+     */
+    public function preprocess(array &$samples)
+    {
+        foreach ($samples as &$sample) {
+            $this->preprocessSample($sample, $samples);
+        }
+    }
+
+    /**
+     * @param array $sample
+     * @param array $samples
+     */
+    private function preprocessSample(array &$sample, array $samples)
+    {
+        foreach ($sample as $column => &$value) {
+            if ($value === $this->missingValue) {
+                $value = $this->strategy->replaceValue($this->getAxis($column, $sample, $samples));
+            }
+        }
+    }
+
+    /**
+     * @param int   $column
+     * @param array $currentSample
+     * @param array $samples
+     * 
+     * @return array
+     */
+    private function getAxis(int $column, array $currentSample, array $samples): array
+    {
+        if (self::AXIS_ROW === $this->axis) {
+            return array_diff($currentSample, [$this->missingValue]);
+        }
+
+        $axis = [];
+        foreach ($samples as $sample) {
+            if ($sample[$column] !== $this->missingValue) {
+                $axis[] = $sample[$column];
+            }
+        }
+
+        return $axis;
+    }
+}

src/Phpml/Preprocessing/Imputer/Strategy.php

@@ -0,0 +1,15 @@
+<?php
+
+declare (strict_types = 1);
+
+namespace Phpml\Preprocessing\Imputer;
+
+interface Strategy
+{
+    /**
+     * @param array $currentAxis
+     *
+     * @return mixed
+     */
+    public function replaceValue(array $currentAxis);
+}

src/Phpml/Preprocessing/Imputer/Strategy/MeanStrategy.php

@@ -0,0 +1,16 @@
+<?php
+
+declare (strict_types = 1);
+
+namespace Phpml\Preprocessing\Imputer\Strategy;
+
+use Phpml\Preprocessing\Imputer\Strategy;
+use Phpml\Math\Statistic\Mean;
+
+class MeanStrategy implements Strategy
+{
+    public function replaceValue(array $currentAxis)
+    {
+        return Mean::arithmetic($currentAxis);
+    }
+}

src/Phpml/Preprocessing/Preprocessor.php

@@ -0,0 +1,13 @@
+<?php
+
+declare (strict_types = 1);
+
+namespace Phpml\Preprocessing;
+
+interface Preprocessor
+{
+    /**
+     * @param array $samples
+     */
+    public function preprocess(array &$samples);
+}

tests/Phpml/Preprocessing/ImputerTest.php

@@ -0,0 +1,55 @@
+<?php
+
+declare (strict_types = 1);
+
+namespace tests\Preprocessing;
+
+use Phpml\Preprocessing\Imputer;
+use Phpml\Preprocessing\Imputer\Strategy\MeanStrategy;
+
+class ImputerTest extends \PHPUnit_Framework_TestCase
+{
+    public function testCompletingMissingValuesWithMeanStrategyOnColumnAxis()
+    {
+        $data = [
+            [1, null, 3, 4],
+            [4, 3, 2, 1],
+            [null, 6, 7, 8],
+            [8, 7, null, 5],
+        ];
+
+        $imputeData = [
+            [1, 5.33, 3, 4],
+            [4, 3, 2, 1],
+            [4.33, 6, 7, 8],
+            [8, 7, 4, 5],
+        ];
+
+        $imputer = new Imputer(null, new MeanStrategy(), Imputer::AXIS_COLUMN);
+        $imputer->preprocess($data);
+
+        $this->assertEquals($imputeData, $data, '', $delta = 0.01);
+    }
+
+    public function testCompletingMissingValuesWithMeanStrategyOnRowAxis()
+    {
+        $data = [
+            [1, null, 3, 4],
+            [4, 3, 2, 1],
+            [null, 6, 7, 8],
+            [8, 7, null, 5],
+        ];
+
+        $imputeData = [
+            [1, 2.66, 3, 4],
+            [4, 3, 2, 1],
+            [7, 6, 7, 8],
+            [8, 7, 6.66, 5],
+        ];
+
+        $imputer = new Imputer(null, new MeanStrategy(), Imputer::AXIS_ROW);
+        $imputer->preprocess($data);
+
+        $this->assertEquals($imputeData, $data, '', $delta = 0.01);
+    }
+}