forgot to add the ngram class itself

git-svn-id: http://google-refine.googlecode.com/svn/trunk@931 7d457c2a-affb-35e4-300a-418c747d4874

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

@@ -0,0 +1,56 @@
+package com.metaweb.gridworks.expr.functions.strings;
+
+import java.util.Properties;
+
+import org.apache.commons.lang.StringUtils;
+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 NGram implements Function {
+
+    public Object call(Properties bindings, Object[] args) {
+        if (args.length == 2) {
+            Object s = args[0];
+            Object n = args[1];
+            
+            if (s != null && s instanceof String && n != null && n instanceof Number) {
+                
+                String[] tokens = StringUtils.split((String) s);
+                
+                int count = ((Number) n).intValue();
+                if (count >= tokens.length) {
+                    return new String[] { (String) s };
+                }
+                
+                int len = tokens.length - count + 1;
+                String[] ngrams = new String[len];
+                for (int i = 0; i < len; i++) {
+                    String[] ss = new String[count];
+                    for (int j = 0; j < count; j++) {
+                        ss[j] = tokens[i + j];
+                    }
+                    ngrams[i] = StringUtils.join(ss,' ');
+                }
+                               
+                return ngrams;
+            }
+            
+            return null;
+        }
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects a string and a number");
+    }
+    
+    public void write(JSONWriter writer, Properties options)
+        throws JSONException {
+    
+        writer.object();
+        writer.key("description"); writer.value("Returns an array of the word ngrams of s");
+        writer.key("params"); writer.value("string s, number n");
+        writer.key("returns"); writer.value("array of strings");
+        writer.endObject();
+    }
+}