Change separator in itemsets

src/FPGrowth.php

@@ -10,8 +10,10 @@ class FPGrowth
 {
     protected int $support = 3;
     protected float $confidence = 0.7;
-
+    private int $maxLength = 0;
+    private $itemsetSeparator;
     private $patterns;
+
     private $rules;
 
     /**
@@ -50,6 +52,15 @@ public function setConfidence(float $confidence): self
         return $this;
     }
 
+    public function getMaxLength(): int
+    {
+        return $this->maxLength;
+    }
+
+    public function setMaxLength(int $maxLength): void
+    {
+        $this->maxLength = $maxLength;
+    }
     /**
      * @return mixed
      */
@@ -71,10 +82,12 @@ public function getRules()
      * @param int $support 1, 2, 3 ...
      * @param float $confidence 0 ... 1
      */
-    public function __construct(int $support, float $confidence)
+    public function __construct(int $support, float $confidence, int $maxLength = 0, string $itemsetSeparator = "\0")
     {
         $this->setSupport($support);
         $this->setConfidence($confidence);
+        $this->setMaxLength($maxLength);
+        $this->itemsetSeparator = $itemsetSeparator;
     }
 
     /**
@@ -93,7 +106,7 @@ public function run(array $transactions)
      */
     protected function findFrequentPatterns(array $transactions): array
     {
-        $tree = new FPTree($transactions, $this->support, null, 0);
+        $tree = new FPTree($transactions, $this->support, null, 0, $this->maxLength, $this->itemsetSeparator);
         return $tree->minePatterns($this->support);
     }
 
@@ -105,16 +118,16 @@ protected function generateAssociationRules(array $patterns): array
     {
         $rules = [];
         foreach (array_keys($patterns) as $pattern) {
-            $itemSet = explode(',', $pattern);
+            $itemSet = explode($this->itemsetSeparator, $pattern);
             $upperSupport = $patterns[$pattern];
             for ($i = 1; $i < count($itemSet); $i++) {
                 $combinations = new Combinations($itemSet, $i);
                 foreach ($combinations->generator() as $antecedent) {
                     sort($antecedent);
-                    $antecedentStr = implode(',', $antecedent);
+                    $antecedentStr = implode($this->itemsetSeparator, $antecedent);
                     $consequent = array_diff($itemSet, $antecedent);
                     sort($consequent);
-                    $consequentStr = implode(',', $consequent);
+                    $consequentStr = implode($this->itemsetSeparator, $consequent);
                     if (isset($patterns[$antecedentStr])) {
                         $lowerSupport = $patterns[$antecedentStr];
                         $confidence = floatval($upperSupport) / $lowerSupport;

src/FPTree.php

@@ -16,18 +16,26 @@ class FPTree
 
     private FPNode $root;
 
+    private int $maxLength = 0;
+
+    private string $itemsetSeparator;
+
+    private int    $depth = 0;
+
     /**
      * Initialize the tree.
      * @param array $transactions
      * @param int $threshold
      * @param $rootValue
      * @param int $rootCount
      */
-    public function __construct(array $transactions, int $threshold, $rootValue, int $rootCount)
+    public function __construct(array $transactions, int $threshold, $rootValue, int $rootCount, $maxLength = 0, string $itemsetSeparator = "\0")
     {
         $this->frequent = $this->findFrequentItems($transactions, $threshold);
         $this->headers = $this->buildHeaderTable();
         $this->root = $this->buildFPTree($transactions, $rootValue, $rootCount, $this->frequent);
+        $this->maxLength = $maxLength;
+        $this->itemsetSeparator = $itemsetSeparator;
     }
 
     /**
@@ -168,6 +176,8 @@ public function minePatterns(int $threshold): array
     {
         if ($this->treeHasSinglePath($this->root)) {
             return $this->generatePatternList();
+        } elseif ($this->maxLength && $this->maxLength <= $this->getDepth()) {
+            return [];
         }
 
         return $this->zipPatterns($this->mineSubTrees($threshold));
@@ -188,10 +198,10 @@ protected function zipPatterns(array $patterns): array
         // We are in a conditional tree.
         $newPatterns = [];
         foreach (array_keys($patterns) as $strKey) {
-            $key = explode(',', $strKey);
+            $key = explode($this->itemsetSeparator, $strKey);
             $key[] = $this->root->value;
             sort($key);
-            $newPatterns[implode(',', $key)] = $patterns[$strKey];
+            $newPatterns[implode($this->itemsetSeparator, $key)] = $patterns[$strKey];
         }
 
         return $newPatterns;
@@ -211,7 +221,13 @@ protected function generatePatternList(): array
             $patterns[$this->root->value] = $this->root->count;
         }
 
-        for ($i = 1; $i <= count($items); $i++) {
+        // limit length of combinations to remaining length
+        $count = count($items);
+        if ($this->maxLength) {
+            $count = min($count, $this->maxLength - $this->getDepth());
+        }
+
+        for ($i = 1; $i <= $count; $i++) {
             $combinations = new Combinations($items,$i);
             foreach ($combinations->generator() as $subset) {
                 $pattern = $this->root->value !== null ? array_merge($subset, [$this->root->value]) : $subset;
@@ -223,7 +239,7 @@ protected function generatePatternList(): array
                         $min = $this->frequent[$x];
                     }
                 }
-                $patterns[implode(',', $pattern)] = $min;
+                $patterns[implode($this->itemsetSeparator, $pattern)] = $min;
             }
         }
 
@@ -270,7 +286,8 @@ protected function mineSubTrees(int $threshold): array
             }
 
             // Now we have the input for a subtree, so construct it and grab the patterns.
-            $subtree = new FPTree($conditionalTreeInput, $threshold, $item, $this->frequent[$item]);
+            $subtree = new FPTree($conditionalTreeInput, $threshold, $item, $this->frequent[$item], $this->maxLength);
+            $subtree->depth = $this->depth + 1;
             $subtreePatterns = $subtree->minePatterns($threshold);
 
             // Insert subtree patterns into main patterns dictionary.
@@ -285,4 +302,9 @@ protected function mineSubTrees(int $threshold): array
 
         return $patterns;
     }
+
+    private function getDepth(): int
+    {
+        return $this->depth;
+    }
 }