tranlyvu/recommender

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""Prove cosine function to calculate cosine"""

from __future__ import division
from math import sqrt

__author__ = "Tran Ly Vu (vutransingapore@gmail.com)"
__copyright__ = "Copyright (c) 2016 - 2019 Tran Ly Vu. All Rights Reserved."
__license__ = "Apache License 2.0"
__credits__ = ["Tran Ly Vu"]
__maintainer__ = "Tran Ly Vu"
__email__ = "vutransingapore@gmail.com"
__status__ = "Beta"

def cosine(preference_space, person1, person2):
    
    """ return cosine similarity measure @ https://en.wikipedia.org/wiki/Cosine_similarity
    
    Args
    --------------
        preference_space (dict) keys are users while values are dictionary of items and ratings
                        ie. preference_space={'userA:{'item1':'ratingA1,'item2':'ratingA2....'itemn':'ratingAn},
                                              'userB:{'item1':'ratingB1,'item2':'ratingB2....'itemn':'ratingBn},
                                               .....
                                              'userZ:{'item1':'ratingZ1,'item2':'ratingZ2....'itemn':'ratingZn},
                                                }

        person1 (str): user id/name
        
        person2 (str): user id/name
        
    Returns
    --------------    
        float
    
    Raises
    --------------
        ZeroDivisionError

    """

    common_interest = [x for x in preference_space[person1] if x in preference_space[person2]]
    vector1 = list(map(lambda x: 1 if x in common_interest else 0, preference_space[person1]))
    vector2 = list(map(lambda x: 1 if x in common_interest else 0, preference_space[person2]))
    
    sumxx = 0
    for i in range(len(vector1)):
        x = vector1[i]
        sumxx += x*x
    
    sumyy = 0
    for i in range(len(vector2)):
        y = vector2[i]
        sumyy += y*y

    denominator = sqrt(sumxx * sumyy)

    numerator = 0
    for i in range(min(len(vector1), len(vector2))):
        x,y = vector1[i], vector2[i]
        numerator += x*y

    if denominator == 0:
        return 0
    else:
        return numerator/denominator