rddsampler.py 文件源码

def getPoissonSample(self, mean):
        # Using Knuth's algorithm described in
        # http://en.wikipedia.org/wiki/Poisson_distribution
        if mean < 20.0:
            # one exp and k+1 random calls
            l = math.exp(-mean)
            p = self._random.random()
            k = 0
            while p > l:
                k += 1
                p *= self._random.random()
        else:
            # switch to the log domain, k+1 expovariate (random + log) calls
            p = self._random.expovariate(mean)
            k = 0
            while p < 1.0:
                k += 1
                p += self._random.expovariate(mean)
        return k