fixed zero hash intersection

examples/intersection-improved-empty.php

@@ -0,0 +1,64 @@
+<?php
+
+include __DIR__ . '/../vendor/autoload.php';
+include __DIR__ . '/randomGenerator.php';
+
+// adjusted so the union is almost the size of the hash k
+$set1 = randomSet(110000);
+
+$set2 = randomSet(0);
+
+$set3 = randomSet(120000);
+
+echo "Number of words in set 1: " . count($set1) . "\n";
+
+echo "Number of words in set 2: " . count($set2) . "\n";
+
+echo "Number of words in set 3: " . count($set3) . "\n";
+
+
+echo "------\n";
+
+echo "Cardinailiy of set 1: " . cardinality($set1) . "\n";
+
+echo "Cardinailiy of set 2: " . cardinality($set2) . "\n";
+
+echo "Cardinailiy of set 3: " . cardinality($set3) . "\n";
+
+$intersection = array_intersect($set1, $set2, $set3);
+
+$union = array_merge($set1, $set2, $set3);
+
+$intersectionCount = cardinality($intersection);
+
+echo "Cardinailiy of union: " . cardinality($union) . "\n";
+
+echo "Cardinailiy of intersection: " . $intersectionCount . "\n";
+
+echo "------\nLogLog\n";
+
+$log_logs = array();
+
+foreach(array($set1, $set2, $set3) as $i => $set)
+{
+    $log_log = new HyperLogLog\MinHash();
+
+    foreach ($set as $word) {
+        $log_log->add($word);
+    }
+
+    $log_logs[] = $log_log;
+
+    echo "Added set " . ($i + 1) . "\n";
+}
+
+$count = \HyperLogLog\Utils\MinHashIntersector::count($log_logs);
+
+echo "intersection complete: count: $count\n";
+
+if($count)
+{
+    echo "Error: 100% - count should be zero\n";
+}
+
+echo "Error: 0% - count is zero\n";

src/HyperLogLog/Utils/MinHashIntersector.php

@@ -27,7 +27,7 @@ public static function count(array $minHashes, $strict = true)
             }
         }
 
-        $intersection = array_intersect($intersection, $totalHll->getMinHash()->toArray());
+        $intersectionCount = count(array_intersect($intersection, $totalHll->getMinHash()->toArray()));
 
         $hllUnionCount = $totalHll->count();
 
@@ -37,12 +37,12 @@ public static function count(array $minHashes, $strict = true)
          * the min hash data structures will be accurate until the size of the union is
          * greater than the max size of the min hash data structure
          */
-        if($hllUnionCount < $minHashK)
+        if($intersectionCount === 0 || $hllUnionCount < $minHashK)
         {
-            return count($intersection);
+            return $intersectionCount;
         }
 
-        return floor((count($intersection) / $minHashK) * $hllUnionCount);
+        return floor($intersectionCount / $minHashK) * $hllUnionCount;
     }
 
     private static function getMinHashKForSet(array $minHashes, $strict)