add the ngramFingerprint function

git-svn-id: http://google-refine.googlecode.com/svn/trunk@191 7d457c2a-affb-35e4-300a-418c747d4874

src/main/java/com/metaweb/gridworks/expr/functions/strings/NGramFingerprint.java

@@ -0,0 +1,61 @@
+package com.metaweb.gridworks.expr.functions.strings;
+
+import java.util.Iterator;
+import java.util.Properties;
+import java.util.TreeSet;
+import java.util.regex.Pattern;
+
+import org.json.JSONException;
+import org.json.JSONWriter;
+
+import com.metaweb.gridworks.expr.EvalError;
+import com.metaweb.gridworks.gel.ControlFunctionRegistry;
+import com.metaweb.gridworks.gel.Function;
+
+public class NGramFingerprint implements Function {
+
+    static final Pattern alphanum = Pattern.compile("\\p{Punct}|\\p{Cntrl}|\\p{Space}");
+    
+    public Object call(Properties bindings, Object[] args) {
+        if (args.length == 1 || args.length == 2) {
+            if (args[0] != null) {
+                int ngram_size = 1;
+                if (args.length == 2 && args[1] != null) {
+                    ngram_size = (args[1] instanceof Number) ? ((Number) args[1]).intValue() : Integer.parseInt(args[1].toString());
+                }
+                Object o = args[0];
+                String s = (o instanceof String) ? (String) o : o.toString(); 
+                s = s.toLowerCase(); // then lowercase it
+                s = alphanum.matcher(s).replaceAll(""); // then remove all punctuation and control chars
+                TreeSet<String> set = ngram_split(s,ngram_size);
+                StringBuffer b = new StringBuffer();
+                Iterator<String> i = set.iterator();
+                while (i.hasNext()) {
+                    b.append(i.next());
+                }
+                return b.toString(); // join ordered fragments back together
+            }
+            return null;
+        }
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects at least a string");
+    }
+
+    protected TreeSet<String> ngram_split(String s, int size) {
+        TreeSet<String> set = new TreeSet<String>();
+        char[] chars = s.toCharArray();
+        for (int i = 0; i + size <= chars.length; i++) {
+            set.add(new String(chars,i,size));
+        }
+        return set;
+    }
+    
+    public void write(JSONWriter writer, Properties options)
+        throws JSONException {
+    
+        writer.object();
+        writer.key("description"); writer.value("Returns the n-gram fingerprint of s");
+        writer.key("params"); writer.value("string s, number n");
+        writer.key("returns"); writer.value("string");
+        writer.endObject();
+    }
+}

src/main/java/com/metaweb/gridworks/gel/ControlFunctionRegistry.java

@@ -34,6 +34,7 @@ import com.metaweb.gridworks.expr.functions.strings.Fingerprint;
 import com.metaweb.gridworks.expr.functions.strings.IndexOf;
 import com.metaweb.gridworks.expr.functions.strings.LastIndexOf;
 import com.metaweb.gridworks.expr.functions.strings.MD5;
+import com.metaweb.gridworks.expr.functions.strings.NGramFingerprint;
 import com.metaweb.gridworks.expr.functions.strings.Partition;
 import com.metaweb.gridworks.expr.functions.strings.Phonetic;
 import com.metaweb.gridworks.expr.functions.strings.RPartition;
@@ -131,6 +132,7 @@ public class ControlFunctionRegistry {
         registerFunction("diff", new Diff());
         registerFunction("chomp", new Diff());
         registerFunction("fingerprint", new Fingerprint());
+        registerFunction("ngramFingerprint", new NGramFingerprint());
         registerFunction("phonetic", new Phonetic());
         registerFunction("reinterpret", new Reinterpret());