均值,方差: 概率质量函数PMF

__author__ = 'dell'

import Pmf
import matplotlib.pyplot as pyplot

pmf = Pmf.MakePmfFromList([1, 2, 2, 3, 5])
print 'Mean by Pmf ', pmf.Mean()
print 'Var by Pmf ', pmf.Var()

def PmfMean(pmf):
    t = [x * v for x, v in pmf.Items()]
    res = sum(t)
    return res

def PmfVar(pmf):
    mu = PmfMean(pmf)
    t = [p * ((v - mu) ** 2) for v, p in pmf.Items()]
    res = sum(t)
    return res

print 'Mean by local ', PmfMean(pmf)
print 'Var by local ', PmfVar(pmf)

运行结果：
D:\Python27\python.exe F:/sync_code/python/survivalanalysis.py
Mean by Pmf  2.6
Var by Pmf  1.84
Mean by local  2.6
Var by local  1.84