#format python
"""SimpleRegressionAnalysis
"""
import unittest, math

class SimpleRegressionAnalyzer:
    """when y = a + b x, 
    and inputdata is [(x1,y1),(x2,y2)...]
    """
    def __init__(self):
        self.r = self.a = self.b = None
    def setData(self, anTwoTuplesList):
        self.data = anTwoTuplesList
        self._regress()

    def _avg(self):
        sumX = sumY = 0
        n = float(len(self.data))
        for eachX, eachY in self.data:
            sumX+=eachX
            sumY+=eachY
        return (sumX/n, sumY/n)

    def _regress(self):
        s_xy = 0; s_xx = 0; s_yy = 0
        avgX, avgY = self._avg()
        for eachX, eachY in self.data:
            xd=eachX-avgX
            yd=eachY-avgY
            s_xy += xd*yd
            s_xx += xd**2
            s_yy += yd**2
        self.b = s_xy / s_xx
        self.a = avgY - self.b * avgX
        try:
            self.r = s_xy / (math.sqrt(s_xx * s_yy))
        except ZeroDivisionError:
            self.r = 0

    def getConstants(self):
        return (self.a, self.b)
    def getCoefficient(self):
        return self.r
    def setConstants(self, a, b):
        self.a = a
        self.b = b
    def setCoefficient(self, r):
        self.r = r
    def getValue(self, x):
        return self.a + self.b * x


class RegressionTest(unittest.TestCase):
    def setUp(self):
        inputData = [(1.0, 1.0), (3.0, 4.0)]
        self.sra = SimpleRegressionAnalyzer(inputData)
    def testAverage(self):
        self.assertEquals((2.0,2.5), self.sra._avg())
    def testGetConstants(self):
        self.assertEquals((-0.5,1.5), self.sra.getConstants())
    def testGetCoefficient(self):
        self.assertEquals(1, self.sra.getCoefficient())
    def testZeroDivision(self):
        self.sra.setData([(1.0,1.0),(2.0,1.0)])
        self.assertEquals(0, self.sra.getCoefficient())

if __name__=='__main__':
    unittest.main(argv=('','-v'))