opennlp-ml/src/main/java/org/apache/opennlp/ml/maxent/BasicEventStream.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 org.apache.opennlp.ml.maxent;

import org.apache.opennlp.ml.model.AbstractEventStream;
import org.apache.opennlp.ml.model.Event;

/**
 * A object which can deliver a stream of training events assuming
 * that each event is represented as a separated list containing
 * all the contextual predicates, with the last item being the
 * outcome. The default separator is the space " ".
 * e.g.: 
 *
 * <p> cp_1 cp_2 ... cp_n outcome
 * <p> cp_1,cp_2,...,cp_n,outcome
 */
public class BasicEventStream extends AbstractEventStream {
  ContextGenerator cg;
  DataStream ds;
  Event next;

  private String separator = " ";
  
   public BasicEventStream (DataStream ds, String sep) {
    separator = sep;
    cg = new BasicContextGenerator(separator);
    this.ds = ds;
    if (this.ds.hasNext())
      next = createEvent((String)this.ds.nextToken());
  }
  
 public BasicEventStream (DataStream ds) {
    this(ds, " ");
  }
  
  /**
   * Returns the next Event object held in this EventStream.  Each call to nextEvent advances the EventStream.
   *
   * @return the Event object which is next in this EventStream
   */
  public Event next () {
    while (next == null && this.ds.hasNext())
      next = createEvent((String)this.ds.nextToken());
    
    Event current = next;
    if (this.ds.hasNext()) {
      next = createEvent((String)this.ds.nextToken());
    }
    else {
      next = null;
    }
    return current;
  }
  
  /**
   * Test whether there are any Events remaining in this EventStream.
   *
   * @return true if this EventStream has more Events
   */
  public boolean hasNext () {
    while (next == null && ds.hasNext())
      next = createEvent((String)ds.nextToken());
    return next != null;
  }
  
  private Event createEvent(String obs) {
    int lastSpace = obs.lastIndexOf(separator);
    if (lastSpace == -1) 
      return null;
    else
      return new Event(obs.substring(lastSpace+1),
          cg.getContext(obs.substring(0, lastSpace)));
  }
  
  
}