#include "gtl_math_var.h"
#include "gtl_math.h"

namespace gtl {
    namespace math {

        var::var(gtl::analog_data *data)
        : analog_value(data)
        , _variance(0.)
        {
            _name = "var";
        }

        void var::before_copying_data(std::vector<qreal>::iterator begin, std::vector<qreal>::iterator end)
        {
            _variance -= variance(begin, end);
        }

        void var::after_copying_data(std::vector<qreal>::iterator begin, std::vector<qreal>::iterator end)
        {
            _variance += variance(begin, end);
        }

        void var::data_changed()
        {
            analog_value::data_changed();
            if(_data.size() != 0)
                _value = _variance;

            emit value_changed();
        }

        qreal var::variance(std::vector<qreal>::iterator begin, std::vector<qreal>::iterator end)
        {
            int n = std::distance(begin, end);

            qreal mean  = std::accumulate(begin, end, 0.)/n;

            qreal v = 0.;
            for(auto it = begin; it != end; ++it)
                v += qPow((*it - mean), 2);
            v /= n-1;

            return v;
        }

    } // namespace math
} // namespace gtl