solr/contrib/ltr/src/java/org/apache/solr/ltr/norm/StandardNormalizer.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.solr.ltr.norm;

import java.util.LinkedHashMap;

/**
 * A Normalizer to scale a feature value around an average-and-standard-deviation distribution.
 * <p>
 * Example configuration:
<pre>
"norm" : {
    "class" : "org.apache.solr.ltr.norm.StandardNormalizer",
    "params" : { "avg":"42", "std":"6" }
}
</pre>
 * <p>
 * Example normalizations:
 * <ul>
 * <li>39 will be normalized to -0.5
 * <li>42 will be normalized to  0
 * <li>45 will be normalized to +0.5
 * </ul>
 */
public class StandardNormalizer extends Normalizer {

  private float avg = 0f;
  private float std = 1f;

  public float getAvg() {
    return avg;
  }

  public void setAvg(float avg) {
    this.avg = avg;
  }

  public float getStd() {
    return std;
  }

  public void setStd(float std) {
    this.std = std;
  }

  public void setAvg(String avg) {
    this.avg = Float.parseFloat(avg);
  }

  public void setStd(String std) {
    this.std = Float.parseFloat(std);
  }

  @Override
  public float normalize(float value) {
    return (value - avg) / std;
  }

  @Override
  protected void validate() throws NormalizerException {
    if (std <= 0f) {
      throw
      new NormalizerException("Standard Normalizer standard deviation must "
          + "be positive | avg = " + avg + ",std = " + std);
    }
  }

  @Override
  public LinkedHashMap<String,Object> paramsToMap() {
    final LinkedHashMap<String,Object> params = new LinkedHashMap<>(2, 1.0f);
    params.put("avg", Float.toString(avg));
    params.put("std", Float.toString(std));
    return params;
  }

  @Override
  public String toString() {
    final StringBuilder sb = new StringBuilder(64); // default initialCapacity of 16 won't be enough
    sb.append(getClass().getSimpleName()).append('(');
    sb.append("avg=").append(avg);
    sb.append(",std=").append(avg).append(')');
    return sb.toString();
  }

}