opennlp.tools.util.featuregen.PrefixFeatureGenerator Maven / Gradle / Ivy
/*
* 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.util.featuregen;
import java.util.List;
public class PrefixFeatureGenerator implements AdaptiveFeatureGenerator {
static final int DEFAULT_MAX_LENGTH = 4;
private final int prefixLength;
public PrefixFeatureGenerator() {
prefixLength = DEFAULT_MAX_LENGTH;
}
public PrefixFeatureGenerator(int prefixLength) {
this.prefixLength = prefixLength;
}
@Override
public void createFeatures(List features, String[] tokens, int index,
String[] previousOutcomes) {
String[] prefs = getPrefixes(tokens[index]);
for (String pref : prefs) {
features.add("pre=" + pref);
}
}
private String[] getPrefixes(String lex) {
int prefixes = Math.min(prefixLength, lex.length());
String[] prefs = new String[prefixes];
for (int li = 0; li < prefixes; li++) {
prefs[li] = lex.substring(0, Math.min(li + 1, lex.length()));
}
return prefs;
}
}