add in document cosine similarity comparison

Author: yooper

src/Comparisons/CosineSimilarityComparison.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace TextAnalysis\Comparisons;
+
+use TextAnalysis\Interfaces\IDistance;
+use TextAnalysis\Interfaces\ISimilarity;
+
+/**
+ * Implements cosine similarity algorithm for comparing two sets of arrays
+ *
+ * @author yooper
+ */
+class CosineSimilarityComparison implements IDistance, ISimilarity 
+{
+    /**
+     * 
+     * @param array $text1 an array of tokens
+     * @param array $text2 an array of tokens
+     */
+    public function similarity($text1, $text2) 
+    {
+        $text1Freq = array_count_values($text1);
+        $text2Freq = array_count_values($text2);
+        $product = 0.0;
+               
+        // always choose the smaller document
+        if(count($text1Freq) > count($text2Freq)) {
+            $iterateTokens =& $text1Freq;
+        } else {
+            $iterateTokens =& $text2Freq;
+        }
+        
+        foreach($iterateTokens as $term => $freq)
+        {
+            if (isset($text1Freq[$term]) && isset($text2Freq[$term])) {
+                $product += $text1Freq[$term] * $text2Freq[$term];
+            }                     
+        }
+        
+        $productFunc = function($carry, $freq) 
+        {
+            $carry += pow($freq, 2);
+            return $carry;
+        };
+           
+        $text1VectorSum = sqrt(array_reduce(array_values($text1Freq), $productFunc, 0));
+        $text2VectorSum = sqrt(array_reduce(array_values($text2Freq), $productFunc, 0));
+        return $product / ($text1VectorSum * $text2VectorSum);
+        
+    }
+
+    /**
+     * 
+     * @param array $text1
+     * @param array $text2
+     * @return float
+     */
+    public function distance($text1, $text2) 
+    {
+        return 1 - $this->similarity($text1, $text2);
+    }
+
+}

tests/TextAnalysis/Comparisons/CosineSimilarityComparisonTest.php

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+<?php
+
+namespace Tests\TextAnalysis\Comparisons;
+
+use TextAnalysis\Comparisons\CosineSimilarityComparison;
+
+/**
+ *
+ * @author yooper
+ */
+class CosineSimilarityComparisonTest extends \PHPUnit_Framework_TestCase
+{
+    public function testIdentical()
+    {
+        $text1 = ["hiking" , "camping", "swimming"];
+        $text2 = ["hiking" , "camping", "swimming"];        
+        $compare = new CosineSimilarityComparison();
+        $this->assertEquals(1.0, $compare->similarity($text1, $text2));
+
+    }
+   
+    public function testDifferent()
+    {
+        $text1 = ["hiking" , "hiking", "camping", "swimming"];
+        $text2 = ["hiking" , "biking", "camping", "swimming"];        
+        $compare = new CosineSimilarityComparison();
+        $this->assertEquals(0.8, round($compare->similarity($text1, $text2), 1));        
+    }
+    
+    public function testNothingInCommon()
+    {
+        $text1 = ["hiking", "camping", "swimming"];
+        $text2 = ["biking", "boating", "floating"];        
+        $compare = new CosineSimilarityComparison();
+        $this->assertEquals(0, $compare->similarity($text1, $text2));         
+    }
+}