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minhash.py
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minhash.py
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import random
import hashlib
import sys
import math
class MinHash(object):
def __init__(self, k):
if k < 1:
raise Exception("Invalid K: number of hash function can't be less than 1")
self.k = k
self.salts = [random.getrandbits(32) for i in range(self.k)]
def similarity(self, A, B):
sigA = self.__signatures(A)
sigB = self.__signatures(B)
return sum(map(lambda x: int(sigA[x] == sigB[x]), range(self.k)))/float(self.k)
def __signatures(self, A):
signature = []
for salt in self.salts:
sig = []
for x in A:
sig.append(self.__h(x, salt))
signature.append(min(sig))
return signature
def __h(self, value, salt):
m = hashlib.md5() #or hashlib.sha1()
m.update(str(value))
m.update(str(salt))
return m.digest()
if __name__ == "__main__":
A = [3,6,9]
B = [2,4,6,8]
for i in range(10, 1000):
score = MinHash(i).similarity(A,B)
if abs(score - 0.142) < 0.0001:
print i, score