def F(data,beta,lam = 0):
    n = data.count() # find the number of (x,y) pairs in data
    regMSE = (data.map(lambda (x,y): f(x, y, beta)).reduce(lambda x, y: x+y))/float(n) + lam*sum(beta**2)
    return regMSE

def test(data,beta):
    m = data.count()  # find the number of (x,y) pairs in testing data
    testMSE = (data.map(lambda (x,y): f(x,y,beta)).reduce(lambda x, y: x+y))/float(m)
    return testMSE