opennlp-tools/src/main/java/opennlp/tools/doccat/NGramFeatureGenerator.java

/*
 * 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.
 */

package opennlp.tools.doccat;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Map;

/**
 * n-gram {@link FeatureGenerator}
 */
public class NGramFeatureGenerator implements FeatureGenerator {

  public Collection<String> extractFeatures(String[] text, Map<String, Object> extraInfo) {

    List<String> features = new ArrayList<String>();

    for (int i = 0; i < text.length - 1; i++) {
      features.add("ng=" + text[i] + ":" + text[i + 1]);
    }

    return features;
  }
}