Histogram.h

/** \file
 * \author Dmitri Naumov
 * \date   Apr. 2012
 * \brief Implementation of Histogram class.
 *
 */

#ifndef BASELIB_HISTOGRAM_H
#define BASELIB_HISTOGRAM_H

#include <algorithm>
#include <cmath>
#include <iterator>
#include <ostream>
#include <vector>

namespace BaseLib
{

/** Basic Histogram implementation.
 *
 * Creates histogram from input data of type \c T.
 */
template <typename T>
class Histogram
{
    public:
    typedef typename std::vector<T> Data;   ///< 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 data 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)
    {
        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();
    }

    /** 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.
     */
    Histogram(std::vector<T> const& data, const unsigned int nr_bins = 16,
        const bool computeHistogram = true)
        : _data(data), _nr_bins(nr_bins)
    {
        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();
    }

    /** Updates histogram using sorted \c _data vector.
     *
     * Start histogram creation with first element. Then find first element in
     * the next histogram bin. Number of elments 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;

        typedef typename Data::const_iterator DataCI;
        DataCI it = _data.begin();
        DataCI itEnd;
        for (unsigned int bin = 0; bin < _nr_bins; bin++) {
            itEnd = std::upper_bound(it, (DataCI)_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& getNrBins() 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
    {
        const std::size_t count_max = *std::max_element(_histogram.begin(), _histogram.end());
        for (unsigned int bin = 0; bin < _nr_bins; ++bin) {
            os << "[" << _min + bin * _bin_width << ", " << _min + (bin + 1) * _bin_width << ")\t";
            os << _histogram[bin] << "\t";

            const int n_stars = std::ceil(line_width * ((double)_histogram[bin]/count_max));
            for (int star = 0; star < n_stars; star++)
                os << "*";
            os << "\n";
        }
    }

    protected:
    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)
{
    os << h.getNrBins() << " "
        << h.getMinimum() << " "
        << h.getMaximum() << " ";
    std::copy(h.getBinCounts().begin(), h.getBinCounts().end(),
            std::ostream_iterator<T>(os, " "));
    return os << std::endl;
}

}   // namespace BaseLib

#endif  // BASELIB_HISTOGRAM_H