#ifndef MATHUTIL_H
#define MATHUTIL_H

#include <QVector>
#include <QtMath>
#include <limits>

namespace Helper {

static double minvec(const QVector<double> &vec)
{
    double val = std::numeric_limits<double>::min();

    for (int i = 0; i < vec.count(); ++i) {
        if (i == 0) {
            val = vec.at(i);
        } else if (val > vec.at(i)) {
            val = vec.at(i);
        }
    }

    return val;
}

static double maxvec(const QVector<double> &vec)
{
    double val = std::numeric_limits<double>::max();

    for (int i = 0; i < vec.count(); ++i) {
        if (i == 0) {
            val = vec.at(i);
        } else if (val < vec.at(i)) {
            val = vec.at(i);
        }
    }

    return val;
}

/// 均值
static double mean(const QVector<double> &vec)
{
    if (vec.count() == 0) {
        return 0;
    }

    double sum = 0;
    for (auto v : vec) {
        sum += v;
    }
    return sum / vec.count();
}

/// 标准差
static double standardDeviation(const QVector<double> &vec)
{
    return qSqrt(standardDeviation(vec));
}

static std::pair<double, double> meanAndStandardDeviation(const QVector<double> &vec)
{
    if (vec.count() == 0) {
        return std::make_pair(0, 0);
    }

    double meanVal = mean(vec);

    double sum = 0;
    for (auto v : vec) {
        sum += qPow(v - meanVal, 2.0);
    }
    return std::make_pair(meanVal, sum / vec.count());
}

/// 方差
static double variance(const QVector<double> &vec)
{
    if (vec.count() == 0) {
        return 0;
    }

    double meanVal = mean(vec);

    double sum = 0;
    for (auto v : vec) {
        sum += qPow(v - meanVal, 2.0);
    }
    return sum / vec.count();
}

static void Standardization(QVector<QVector<double>> &v)
{
    double Avg, STD;
    for (int i = 0; i < v.size(); i++) {
        Avg = mean(v[i]);
        STD = standardDeviation(v[i]);
        for (int j = 0; j < v[i].size(); j++) {
            v[i][j] = (v[i][j] - Avg) / STD;
        }
    }
}

static double cov(QVector<double> vA, QVector<double> vB)
{
    double total;
    for (int i = 0; i < vA.size(); i++) {
        total += vA[i] * vB[i];
    }
    return (total / vA.size());
}

static QVector<QVector<double>> Covarience(QVector<QVector<double>> features)
{
    QVector<QVector<double>> covMatrix;
    QVector<double> temp;
    for (int i = 0; i < features.size(); i++) {
        for (int j = 0; j < features.size(); j++) {
            temp.push_back(cov(features[i], features[j]));
        }
        covMatrix.push_back(temp);
        temp.clear();
    }

    return covMatrix;
}

}  // namespace Helper
#endif  // MATHUTIL_H