Histogram.h

/**
 * \file
 * \author Dmitrij Naumov
 * \brief Implementation of Histogram class.
 *
 * \copyright
 * Copyright (c) 2012-2025, OpenGeoSys Community (http://www.opengeosys.org)
 *            Distributed under a Modified BSD License.
 *              See accompanying file LICENSE.txt or
 *              http://www.opengeosys.org/project/license
 */

#pragma once

#include <algorithm>
#include <cstddef>
#include <iosfwd>
#include <iterator>
#include <string>
#include <utility>
#include <vector>

namespace BaseLib
{
/** Basic Histogram implementation.
 *
 * Creates histogram from input data of type \c T.
 */
template <typename T>
class Histogram
{
public:
    using Data =
        typename std::vector<double>;  /// Underlying input data vector type.

public:
    /** Creates histogram of the given element in the range \c [first, last).
     *
     * Input data is copied into \c std::vector.
     *
     * \param first Range of elements to create histogram from.
     * \param last Range of elements to create histogram from.
     * \param nr_bins Number of bins in histogram.
     * \param computeHistogram Compute histogram if set. If not set user must
     *        call \c update() before accessing data.
     */
    template <typename InputIterator>
    Histogram(InputIterator first, InputIterator last, const int nr_bins = 16,
              const bool computeHistogram = true)
        : data_(first, last), nr_bins_(nr_bins), dirty_(true)
    {
        init(computeHistogram);
    }

    /** Creates histogram from \c std::vector.
     * \param data Input vector.
     * \param nr_bins Number of bins in histogram.
     * \param computeHistogram Compute histogram if set. If not set user must
     * call \c update() before accessing data.
     */
    explicit Histogram(std::vector<T> data, const unsigned int nr_bins = 16,
                       const bool computeHistogram = true)
        : data_(std::move(data)), nr_bins_(nr_bins), dirty_(true)
    {
        init(computeHistogram);
    }

    /** Updates histogram using sorted \c data_ vector.
     *
     * Start histogram creation with first element. Then find first element in
     * the next histogram bin. Number of elements in the bin is the difference
     * between these two iterators.
     * \verbatim
       [0.1, 0.2, ..., 0.7 , ..., 0.7+binWidth = 0.9,  1.0  , ..., last]
                       it             itEnd - 1      itEnd
       \endverbatim
     */
    void update()
    {
        if (!dirty_)
        {
            return;
        }

        bin_width_ = (max_ - min_) / nr_bins_;

        auto it = data_.begin();
        for (unsigned int bin = 0; bin < nr_bins_; bin++)
        {
            auto itEnd = std::upper_bound(it, data_.end(),
                                          min_ + (bin + 1) * bin_width_);
            histogram_[bin] = std::distance(it, itEnd);
            it = itEnd;
        }
        dirty_ = false;
    }

    void setMinimum(const T& minimum)
    {
        min_ = minimum;
        dirty_ = true;
    }
    void setMaximum(const T& maximum)
    {
        max_ = maximum;
        dirty_ = true;
    }

    const Data& getSortedData() const { return data_; }
    const std::vector<std::size_t>& getBinCounts() const { return histogram_; }
    const unsigned int& getNumberOfBins() const { return nr_bins_; }
    const T& getMinimum() const { return min_; }
    const T& getMaximum() const { return max_; }
    const T& getBinWidth() const { return bin_width_; }

    void prettyPrint(std::ostream& os,
                     const unsigned int line_width = 16) const;

    int write(std::string const& file_name, std::string const& data_set_name,
              std::string const& param_name) const;

protected:
    /** Initialize class members after constructor call.
     */
    void init(const bool computeHistogram = true)
    {
        std::sort(data_.begin(), data_.end());
        histogram_.resize(nr_bins_);
        min_ = data_.front();
        max_ = data_.back();
        bin_width_ = (max_ - min_) / nr_bins_;

        dirty_ = true;
        if (computeHistogram)
        {
            update();
        }
    }

    Data data_;
    const unsigned int nr_bins_;
    std::vector<std::size_t> histogram_;
    T min_, max_;  ///< Minimum and maximum input data values.
    T bin_width_;

private:
    bool dirty_;  ///< When set \c update() will recompute histogram.
};

/** Writes histogram to output stream.
 *
 * Writes histogram properties in this order:
 * number of bins, minimum, maximum, bin0 count, ..., binN-1 count.
 */
template <typename T>
std::ostream& operator<<(std::ostream& os, const Histogram<T>& h);

extern template class Histogram<double>;
extern template std::ostream& operator<<(std::ostream& os,
                                         const Histogram<double>& h);
}  // namespace BaseLib