lucene/suggest/src/test/org/apache/lucene/search/suggest/Average.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.lucene.search.suggest;

import java.util.List;
import java.util.Locale;

/** Average with standard deviation. */
final class Average {
  /** Average (in milliseconds). */
  public final double avg;

  /** Standard deviation (in milliseconds). */
  public final double stddev;

  /** */
  Average(double avg, double stddev) {
    this.avg = avg;
    this.stddev = stddev;
  }

  @Override
  public String toString() {
    return String.format(Locale.ROOT, "%.0f [+- %.2f]", avg, stddev);
  }

  static Average from(List<Double> values) {
    double sum = 0;
    double sumSquares = 0;

    for (double l : values) {
      sum += l;
      sumSquares += l * l;
    }

    double avg = sum / (double) values.size();
    return new Average(
        (sum / (double) values.size()), Math.sqrt(sumSquares / (double) values.size() - avg * avg));
  }
}