pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / contrib / analyzers / common / src / java / org / apache / lucene / analysis / ar / ArabicStemmer.java

diff --git a/lucene-java-3.5.0/lucene/contrib/analyzers/common/src/java/org/apache/lucene/analysis/ar/ArabicStemmer.java b/lucene-java-3.5.0/lucene/contrib/analyzers/common/src/java/org/apache/lucene/analysis/ar/ArabicStemmer.java
new file mode 100644 (file)
index 0000000..c52916e
--- /dev/null
+++ b/lucene-java-3.5.0/lucene/contrib/analyzers/common/src/java/org/apache/lucene/analysis/ar/ArabicStemmer.java
@@ -0,0 +1,150 @@
+package org.apache.lucene.analysis.ar;
+
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import static org.apache.lucene.analysis.util.StemmerUtil.*;
+
+/**
+ *  Stemmer for Arabic.
+ *  <p>
+ *  Stemming  is done in-place for efficiency, operating on a termbuffer.
+ *  <p>
+ *  Stemming is defined as:
+ *  <ul>
+ *  <li> Removal of attached definite article, conjunction, and prepositions.
+ *  <li> Stemming of common suffixes.
+ * </ul>
+ *
+ */
+public class ArabicStemmer {
+  public static final char ALEF = '\u0627';
+  public static final char BEH = '\u0628';
+  public static final char TEH_MARBUTA = '\u0629';
+  public static final char TEH = '\u062A';
+  public static final char FEH = '\u0641';
+  public static final char KAF = '\u0643';
+  public static final char LAM = '\u0644';
+  public static final char NOON = '\u0646';
+  public static final char HEH = '\u0647';
+  public static final char WAW = '\u0648';
+  public static final char YEH = '\u064A';
+  
+  public static final char prefixes[][] = {
+      ("" + ALEF + LAM).toCharArray(), 
+      ("" + WAW + ALEF + LAM).toCharArray(), 
+      ("" + BEH + ALEF + LAM).toCharArray(),
+      ("" + KAF + ALEF + LAM).toCharArray(),
+      ("" + FEH + ALEF + LAM).toCharArray(),
+      ("" + LAM + LAM).toCharArray(),
+      ("" + WAW).toCharArray(),
+  };
+  
+  public static final char suffixes[][] = {
+    ("" + HEH + ALEF).toCharArray(), 
+    ("" + ALEF + NOON).toCharArray(), 
+    ("" + ALEF + TEH).toCharArray(), 
+    ("" + WAW + NOON).toCharArray(), 
+    ("" + YEH + NOON).toCharArray(), 
+    ("" + YEH + HEH).toCharArray(),
+    ("" + YEH + TEH_MARBUTA).toCharArray(),
+    ("" + HEH).toCharArray(),
+    ("" + TEH_MARBUTA).toCharArray(),
+    ("" + YEH).toCharArray(),
+};
+  
+  /**
+   * Stem an input buffer of Arabic text.
+   * 
+   * @param s input buffer
+   * @param len length of input buffer
+   * @return length of input buffer after normalization
+   */
+  public int stem(char s[], int len) {
+    len = stemPrefix(s, len);
+    len = stemSuffix(s, len);
+    
+    return len;
+  }
+  
+  /**
+   * Stem a prefix off an Arabic word.
+   * @param s input buffer
+   * @param len length of input buffer
+   * @return new length of input buffer after stemming.
+   */
+  public int stemPrefix(char s[], int len) {
+    for (int i = 0; i < prefixes.length; i++) 
+      if (startsWithCheckLength(s, len, prefixes[i]))
+        return deleteN(s, 0, len, prefixes[i].length);
+    return len;
+  }
+
+  /**
+   * Stem suffix(es) off an Arabic word.
+   * @param s input buffer
+   * @param len length of input buffer
+   * @return new length of input buffer after stemming
+   */
+  public int stemSuffix(char s[], int len) {
+    for (int i = 0; i < suffixes.length; i++) 
+      if (endsWithCheckLength(s, len, suffixes[i]))
+        len = deleteN(s, len - suffixes[i].length, len, suffixes[i].length);
+    return len;
+  }
+  
+  /**
+   * Returns true if the prefix matches and can be stemmed
+   * @param s input buffer
+   * @param len length of input buffer
+   * @param prefix prefix to check
+   * @return true if the prefix matches and can be stemmed
+   */
+  boolean startsWithCheckLength(char s[], int len, char prefix[]) {
+    if (prefix.length == 1 && len < 4) { // wa- prefix requires at least 3 characters
+      return false;
+    } else if (len < prefix.length + 2) { // other prefixes require only 2.
+      return false;
+    } else {
+      for (int i = 0; i < prefix.length; i++)
+        if (s[i] != prefix[i])
+          return false;
+        
+      return true;
+    }
+  }
+  
+  /**
+   * Returns true if the suffix matches and can be stemmed
+   * @param s input buffer
+   * @param len length of input buffer
+   * @param suffix suffix to check
+   * @return true if the suffix matches and can be stemmed
+   */
+  boolean endsWithCheckLength(char s[], int len, char suffix[]) {
+    if (len < suffix.length + 2) { // all suffixes require at least 2 characters after stemming
+      return false;
+    } else {
+      for (int i = 0; i < suffix.length; i++)
+        if (s[len - suffix.length + i] != suffix[i])
+          return false;
+        
+      return true;
+    }
+  }  
+}