using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Science.Statistics.BasicStatistics
{
    public class Regression
    {
        public Regression()
        {
        }
        private double r, ax, sdx, ay, sdy, err;
        public Regression(DataForScatterDiagram data)
        {
            data.FindStandardDeviationAndAverage();
            Correlation cor = new Correlation(data);
            r = cor.Value;
            ax = data.XStandardDeviationAndAverage.Average;
            sdx = data.XStandardDeviationAndAverage.StandardDeviation;
            ay = data.YStandardDeviationAndAverage.Average;
            sdy = data.YStandardDeviationAndAverage.StandardDeviation;
            err = Math.Sqrt(1.0 - r * r) * sdy;
            FindRegressionLine();
        }
        public Regression(double xAverage, double xStandardDeviation,
            double yAverage, double yStandardDeviation, 
            double correlation)
        {
            ax = xAverage;
            sdx = xStandardDeviation;
            ay = yAverage;
            sdy = yStandardDeviation;
            r = correlation;
            err = Math.Sqrt(1.0 - r * r) * sdy;
            FindRegressionLine();
        }
        private Function.ToLastType<double, double> l;
        public Function.ToLastType<double, double> RegressionLine
        {
            get { return l; }
        }
        public double RootMeanSquareErrorOfY
        {
            get { return err; }
        }
        private void FindRegressionLine()
        {
            a = r * sdy / sdx;
            b = ay - a * ax;
            l = new Function.ToLastType<double, double>(f);            
        }
        public double PredictedYFromX(double x)
        {
            return l(x);
        }
        private double a, b;
        private double f(double x)
        {
            return a * x + b;
        }
    }
}