fix ngram logic

languagetool-dev/src/main/java/org/languagetool/dev/errorcorpus/TrainingDataGenerator.java

@@ -254,11 +254,10 @@ private int getLastPosition(Sentence sentence, String token) {
     return pos;
   }
 
-  private List<String> getContext(Sentence sentence, int pos, String newToken, int toLeft, int toRight) {
-    String plainText = sentence.getText();
+  List<String> getContext(String plainText, int pos, String newToken, int toLeft, int toRight) {
     List<String> tokens = removeWhitespaceTokens(tokenizer.tokenize(plainText));
     List<String> result = new ArrayList<>();
-    for (int i = 1; i > 0 && i <= toLeft; i++) {
+    for (int i = toLeft; i > 0 && i <= toLeft; i--) {
       if (pos-i < 0 ) {
         result.add(LanguageModel.GOOGLE_SENTENCE_START);  // NOTE: only in v2 of the data!
       } else {
@@ -281,12 +280,13 @@ private double[] getFeatures(Sentence sentence, String token, String newToken) {
 
     int position = getLastPosition(sentence, token);
 
-    double ngram2Left = getCountForTuple(getContext(sentence, position, newToken, 1, 0), maxVal);
-    double ngram2Right = getCountForTuple(getContext(sentence, position, newToken, 0, 1), maxVal);
+    String text = sentence.getText();
+    double ngram2Left = getCountForTuple(getContext(text, position, newToken, 1, 0), maxVal);
+    double ngram2Right = getCountForTuple(getContext(text, position, newToken, 0, 1), maxVal);
 
-    double ngram3Left = getCountForTriple(getContext(sentence, position, newToken, 0, 2), maxVal);
-    double ngram3Middle = getCountForTriple(getContext(sentence, position, newToken, 1, 1), maxVal);
-    double ngram3Right = getCountForTriple(getContext(sentence, position, newToken, 2, 0), maxVal);
+    double ngram3Left = getCountForTriple(getContext(text, position, newToken, 0, 2), maxVal);
+    double ngram3Middle = getCountForTriple(getContext(text, position, newToken, 1, 1), maxVal);
+    double ngram3Right = getCountForTriple(getContext(text, position, newToken, 2, 0), maxVal);
 
     return new double[] {ngram2Left, ngram2Right, ngram3Middle, ngram3Left, ngram3Right};
   }

languagetool-dev/src/test/java/org/languagetool/dev/errorcorpus/TrainingDataGeneratorTest.java

@@ -0,0 +1,52 @@
+/* LanguageTool, a natural language style checker 
+ * Copyright (C) 2015 Daniel Naber (http://www.danielnaber.de)
+ * 
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
+ * USA
+ */
+package org.languagetool.dev.errorcorpus;
+
+import org.junit.Test;
+import org.languagetool.language.English;
+import org.languagetool.languagemodel.LanguageModel;
+
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThat;
+
+public class TrainingDataGeneratorTest {
+
+  @Test
+  public void test() {
+    TrainingDataGenerator prg = new TrainingDataGenerator(new English(), new FakeLanguageModel());
+    assertThat(prg.getContext("This is a test.", 2, "XX", 1, 1).toString(), is("[is, XX, test]"));
+    assertThat(prg.getContext("This is a test.", 2, "XX", 0, 2).toString(), is("[XX, test, _END_]"));
+    assertThat(prg.getContext("This is a test.", 2, "XX", 2, 0).toString(), is("[This, is, XX]"));
+    assertThat(prg.getContext("This is a test.", 2, "XX", 3, 0).toString(), is("[_START_, This, is, XX]"));
+  }
+
+  static class FakeLanguageModel implements LanguageModel {
+    @Override
+    public long getCount(String token1, String token2) {
+      return 1;
+    }
+    @Override
+    public long getCount(String token1, String token2, String token3) {
+      return 2;
+    }
+    @Override
+    public void close() {}
+  }
+
+}