Flajolet和Martin算法的python实现

Question

下面是我编写的实现^{}的代码。我使用Jenkins hash function来生成32 bit hash value的数据。程序似乎遵循了算法，但偏离了大约20%。我的数据集由200000多个唯一记录组成，而程序输出约160000个唯一记录。请帮助我理解我所犯的错误。哈希函数按Bob Jerkins' website实现。在

import numpy as np
from jenkinshash import jhash

class PCSA():
    def __init__(self, nmap, maxlength):
        self.nmap = nmap
        self.maxlength = maxlength
        self.bitmap = np.zeros((nmap, maxlength), dtype=np.int)

    def count(self, data):
        hashedValue = jhash(data)
        indexAlpha = hashedValue % self.nmap
        ix = hashedValue / self.nmap
        ix = bin(ix)[2:][::-1]       
        indexBeta = ix.find("1")    #find index of lsb
        if self.bitmap[indexAlpha, indexBeta] == 0:
            self.bitmap[indexAlpha, indexBeta] = 1


    def getCardinality(self):
        sumIx = 0
        for row in range(self.nmap):
            sumIx += np.where(self.bitmap[row, :] == 0)[0][0]

        A = sumIx / self.nmap

        cardinality = self.nmap * (2 ** A)/ MAGIC_CONST

        return cardinality

Answer 1

如果在Python2中运行这个函数，那么计算A的除法可能会导致A变为整数。在

如果是这样，您可以尝试更改：

A = sumIx / self.nmap

到

^{pr2}$