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Genome Damage and Stability Centre SMLM Package Software for single molecule localisation microscopy (SMLM)
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/*-
 * #%L
 * Genome Damage and Stability Centre SMLM Package
 *
 * Software for single molecule localisation microscopy (SMLM)
 * %%
 * Copyright (C) 2011 - 2023 Alex Herbert
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program.  If not, see
 * .
 * #L%
 */

package uk.ac.sussex.gdsc.smlm.function;

import java.util.Arrays;
import uk.ac.sussex.gdsc.core.data.DataException;
import uk.ac.sussex.gdsc.core.utils.MathUtils;

/**
 * Utility class for functions.
 */
public final class FunctionHelper {
  /** No instances. */
  private FunctionHelper() {}

  /**
   * Gets the mean value using a fraction of the cumulative value, when values are sorted in
   * descending order. All values must be positive. The input values are modified by sorting.
   *
   * If {@code fraction <= 0} then the max value is returned. If {@code fraction >=1} then the
   * mean of the data is returned.
   *
   * @param values the values
   * @param fraction the fraction
   * @return the mean value
   * @throws DataException if the values are not positive.
   */
  public static double getMeanValue(double[] values, double fraction) {
    if (fraction <= 0) {
      return MathUtils.max(values);
    }
    double sum = 0;
    for (final double v : values) {
      if (v < 0) {
        throw new DataException("Values must be positive");
      }
      sum += v;
    }
    if (fraction >= 1) {
      return sum / values.length;
    }
    final double target = sum * fraction;
    sum = 0;
    Arrays.sort(values);
    for (int i = values.length; i-- > 0;) {
      sum += values[i];
      if (sum >= target) {
        // Interpolate the count X to obtain the target
        final int x = values.length - i;
        return target / MathUtils.interpolateX(x - 1, sum - values[i], x, sum, target);
      }
    }
    // Edge case
    return sum / values.length;
  }

  /**
   * Gets the x-value corresponding to a fraction of the cumulative value, when values are sorted in
   * descending order. All values must be positive. The input values are modified by sorting.
   *
   * If {@code fraction <= 0} then zero is returned. If {@code fraction >= 1} then data.length is
   * returned.
   *
   * @param values the values
   * @param fraction the fraction
   * @return the x-value
   * @throws DataException if the values are not positive.
   */
  public static double getXValue(double[] values, double fraction) {
    if (fraction <= 0) {
      return 0;
    }
    if (fraction >= 1) {
      return values.length;
    }
    double sum = 0;
    for (final double v : values) {
      if (v < 0) {
        throw new DataException("Values must be positive");
      }
      sum += v;
    }
    final double target = sum * fraction;
    sum = 0;
    Arrays.sort(values);
    for (int i = values.length; i-- > 0;) {
      sum += values[i];
      if (sum >= target) {
        // Interpolate the count X to obtain the target
        final int x = values.length - i;
        return MathUtils.interpolateX(x - 1, sum - values[i], x, sum, target);
      }
    }
    // Edge case
    return values.length;
  }
}