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

namespace Science.Statistics.BasicStatistics
{
    public class Correlation
    {
        public Correlation()
        {
        }
        private DataForScatterDiagram d;
        public DataForScatterDiagram Data
        {
            get { return d; }
            set { d = value; }
        }
        public Correlation(DataForScatterDiagram data)
        {
            int j, n = data.XData.Count;

            for (r = 0.0, j = 0; j < n; j++) r += data.XData[j]*data.YData[j];
            r /= (double)n;
            r -= data.XStandardDeviationAndAverage.Average * data.YStandardDeviationAndAverage.Average;
            r /= data.XStandardDeviationAndAverage.StandardDeviation * data.YStandardDeviationAndAverage.StandardDeviation;
        }
        private double r;
        public double Value
        {
            get { return r; }
            set { r = value; }
        }
        public static Correlation Add(Correlation first, Correlation second)
        {
            Correlation third = new Correlation();

            StandardDeviationAndAverage xsda = StandardDeviationAndAverage.Add(
                first.Data.XStandardDeviationAndAverage, second.Data.XStandardDeviationAndAverage);
            StandardDeviationAndAverage ysda = StandardDeviationAndAverage.Add(
                first.Data.YStandardDeviationAndAverage, second.Data.YStandardDeviationAndAverage);

            int n = first.Data.XStandardDeviationAndAverage.LengthOfData
                + second.Data.XStandardDeviationAndAverage.LengthOfData;

            double fs = first.Value * first.Data.XStandardDeviationAndAverage.StandardDeviation
                * first.Data.YStandardDeviationAndAverage.StandardDeviation;
            fs += first.Data.XStandardDeviationAndAverage.Average
                * first.Data.YStandardDeviationAndAverage.Average;
            fs *= first.Data.XStandardDeviationAndAverage.LengthOfData;

            double ss = second.Value * second.Data.XStandardDeviationAndAverage.StandardDeviation
                * second.Data.YStandardDeviationAndAverage.StandardDeviation;
            ss += second.Data.XStandardDeviationAndAverage.Average
                * second.Data.YStandardDeviationAndAverage.Average;
            ss *= second.Data.XStandardDeviationAndAverage.LengthOfData;

            third.Value = ((fs + ss) / (double)n - xsda.Average * ysda.Average )
                / xsda.StandardDeviation / ysda.StandardDeviation;
            return third;
        }
    }
}