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docs/snippets/php/utils/keyword_extraction_example.php

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+```php title="keyword_extraction_example.php"
+<?php
+
+declare(strict_types=1);
+
+/**
+ * Keyword Extraction Example
+ *
+ * Extract keywords from documents using various algorithms.
+ * Demonstrates automatic keyword detection for document analysis and indexing.
+ */
+
+require_once __DIR__ . '/vendor/autoload.php';
+
+use Kreuzberg\Kreuzberg;
+use Kreuzberg\Config\ExtractionConfig;
+use Kreuzberg\Config\KeywordConfig;
+use Kreuzberg\Enums\KeywordAlgorithm;
+
+$config = new ExtractionConfig(
+    keywords: new KeywordConfig(
+        algorithm: KeywordAlgorithm::YAKE,
+        maxKeywords: 10,
+        minScore: 0.3
+    )
+);
+
+$kreuzberg = new Kreuzberg($config);
+$result = $kreuzberg->extractFile('research_paper.pdf');
+
+echo "Keyword Extraction Results:\n";
+echo str_repeat('=', 60) . "\n";
+echo "Document: research_paper.pdf\n";
+echo "Content length: " . strlen($result->content) . " characters\n\n";
+
+$keywords = $result->metadata['keywords'] ?? [];
+
+if (!empty($keywords)) {
+    echo "Extracted Keywords:\n";
+    echo str_repeat('-', 40) . "\n";
+
+    foreach ($keywords as $keyword) {
+        $text = $keyword['text'] ?? '';
+        $score = $keyword['score'] ?? 0.0;
+        $frequency = $keyword['frequency'] ?? null;
+
+        echo sprintf("  %-30s  Score: %.3f", $text, $score);
+
+        if ($frequency !== null) {
+            echo sprintf("  (appears %d times)", $frequency);
+        }
+
+        echo "\n";
+    }
+    echo "\n";
+} else {
+    echo "No keywords extracted. Try adjusting minScore or maxKeywords.\n\n";
+}
+
+$algorithms = [
+    'YAKE' => KeywordAlgorithm::YAKE,
+    'TextRank' => KeywordAlgorithm::TEXT_RANK,
+    'TF-IDF' => KeywordAlgorithm::TF_IDF,
+];
+
+echo "Algorithm Comparison:\n";
+echo str_repeat('=', 60) . "\n";
+
+foreach ($algorithms as $name => $algorithm) {
+    $algoConfig = new ExtractionConfig(
+        keywords: new KeywordConfig(
+            algorithm: $algorithm,
+            maxKeywords: 5,
+            minScore: 0.2
+        )
+    );
+
+    $kreuzberg = new Kreuzberg($algoConfig);
+    $result = $kreuzberg->extractFile('article.pdf');
+
+    $keywords = $result->metadata['keywords'] ?? [];
+
+    echo "$name algorithm:\n";
+
+    if (!empty($keywords)) {
+        foreach ($keywords as $keyword) {
+            echo "  - {$keyword['text']} ({$keyword['score']})\n";
+        }
+    } else {
+        echo "  No keywords extracted\n";
+    }
+
+    echo "\n";
+}
+
+function categorizeDocument(array $keywords): string
+{
+    $categories = [
+        'technical' => ['algorithm', 'system', 'implementation', 'performance', 'architecture'],
+        'business' => ['revenue', 'market', 'customer', 'strategy', 'investment'],
+        'scientific' => ['research', 'study', 'analysis', 'experiment', 'hypothesis'],
+        'legal' => ['contract', 'agreement', 'liability', 'clause', 'provision'],
+    ];
+
+    $scores = [];
+    foreach ($categories as $category => $terms) {
+        $scores[$category] = 0;
+
+        foreach ($keywords as $keyword) {
+            $keywordText = strtolower($keyword['text'] ?? '');
+            $keywordScore = $keyword['score'] ?? 0.0;
+
+            foreach ($terms as $term) {
+                if (str_contains($keywordText, $term)) {
+                    $scores[$category] += $keywordScore;
+                }
+            }
+        }
+    }
+
+    arsort($scores);
+    $topCategory = array_key_first($scores);
+
+    return $topCategory ?? 'uncategorized';
+}
+
+if (!empty($keywords)) {
+    $category = categorizeDocument($keywords);
+    echo "Document Category: " . ucfirst($category) . "\n\n";
+}
+
+$documents = [
+    'tech_article.pdf',
+    'business_report.pdf',
+    'research_paper.pdf',
+];
+
+$keywordConfig = new ExtractionConfig(
+    keywords: new KeywordConfig(
+        algorithm: KeywordAlgorithm::YAKE,
+        maxKeywords: 8,
+        minScore: 0.25
+    )
+);
+
+$kreuzberg = new Kreuzberg($keywordConfig);
+
+echo "Batch Keyword Extraction:\n";
+echo str_repeat('=', 60) . "\n";
+
+foreach ($documents as $document) {
+    if (!file_exists($document)) {
+        echo "$document: File not found\n\n";
+        continue;
+    }
+
+    $result = $kreuzberg->extractFile($document);
+    $keywords = $result->metadata['keywords'] ?? [];
+
+    echo basename($document) . ":\n";
+
+    if (!empty($keywords)) {
+        $topKeywords = array_slice($keywords, 0, 5);
+        $keywordTexts = array_column($topKeywords, 'text');
+        echo "  Top keywords: " . implode(', ', $keywordTexts) . "\n";
+
+        $category = categorizeDocument($keywords);
+        echo "  Category: " . ucfirst($category) . "\n";
+    } else {
+        echo "  No keywords extracted\n";
+    }
+
+    echo "\n";
+}
+
+$keywordIndex = [];
+
+foreach ($documents as $document) {
+    if (!file_exists($document)) {
+        continue;
+    }
+
+    $result = $kreuzberg->extractFile($document);
+    $keywords = $result->metadata['keywords'] ?? [];
+
+    foreach ($keywords as $keyword) {
+        $text = strtolower($keyword['text'] ?? '');
+        if (!isset($keywordIndex[$text])) {
+            $keywordIndex[$text] = [];
+        }
+        $keywordIndex[$text][] = basename($document);
+    }
+}
+
+echo "Keyword Index (for search):\n";
+echo str_repeat('=', 60) . "\n";
+foreach (array_slice($keywordIndex, 0, 10) as $keyword => $docs) {
+    echo "$keyword: " . implode(', ', array_unique($docs)) . "\n";
+}
+```