/
algos.py
58 lines (40 loc) · 1.39 KB
/
algos.py
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from math import sqrt
#ten times better algorithm
def sim_distance(prefs, person1, person2):
#fetch prefs only once.
firstPerson = prefs(person1)
secondPerson = prefs(person2)
si = []
for movie1 in firstPerson:
if movie1 in secondPerson:
si.append(1)
n = len(si)
if n is 0: return 0
sum_of_squares = sum([pow(firstPerson[item] - secondPerson[item], 2)
for item in firstPerson if item in secondPerson])
return 1/(1+sum_of_squares)
def sim_pearson(prefs, person1, person2):
si = {}
firstPerson = prefs(person1)
secondPerson = prefs(person2)
for item in firstPerson:
if item in secondPerson:
si[item] = 1
n = len(si)
if n is 0: return 0
def square_minus(square, sum, n):
return square-pow(sum, 2)/n
def sum_person(person):
return sum([person[it] for it in si])
def pow_sum_person(person):
return sum([pow(person[it], 2) for it in si])
sum1 = sum_person(firstPerson)
sum2 = sum_person(secondPerson)
sum1Sq = pow_sum_person(firstPerson)
sum2Sq = pow_sum_person(secondPerson)
pSum = sum([firstPerson[it] * secondPerson[it] for it in si])
num = pSum - (sum1*sum2/n)
den = sqrt(square_minus(sum1Sq, sum1, n) * square_minus(sum2Sq, sum2, n))
if den == 0: return 0
r=num/den
return r