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/*
 * (c) 2005 David B. Bracewell
 *
 * 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 com.davidbracewell.apollo.ml.classification;

import com.davidbracewell.apollo.Optimum;
import com.davidbracewell.apollo.linear.NDArray;
import lombok.NonNull;

/**
 * A decision stump, or Zero-One rule, classifier which makes its classification based on the value of a single
 * feature. Acts as weak learner for ensemble techniques like {@link BaggingLearner}
 *
 * @author David B. Bracewell
 */
public class DecisionStump extends Classifier {
   private static final long serialVersionUID = 1L;
   int featureId;
   double featureValue;
   double[] lowerDecision;
   double[] upperDecision;

   protected DecisionStump(ClassifierLearner learner) {
      super(learner);
   }


   @Override
   public Classification classify(@NonNull NDArray vector) {
      double[] distribution;
      if (vector.get(featureId) > featureValue) {
         distribution = upperDecision;
      } else {
         distribution = lowerDecision;
      }
      return createResult(distribution);
   }

   @Override
   public String toString() {
      String lowerAnswer = decodeLabel(Optimum.MAXIMUM.optimumIndex(lowerDecision)).toString();
      String upperAnswer = decodeLabel(Optimum.MAXIMUM.optimumIndex(upperDecision)).toString();
      return "DecisionStump: IF(" + decodeFeature(featureId)
                + " > " + featureValue + ") THEN "
                + upperAnswer + " ELSE " + lowerAnswer + "";
   }
}//END OF DecisionStump