gistfile1.py

critics = {
    'Lisa Rose': {
        'Lady in the water': 2.5,
        'Snakes on a plane': 3.5,
        'Just my luck': 3.0,
        'Superman returns': 3.5,
        'You, Me and Dupree': 2.5,
        'The night listener': 3.0,
    },
    'Gene Seymoud': {
        'Lady in the water': 3.0,
        'Snakes on a plane': 3.5,
        'Just my luck': 3.0,
        'Superman returns': 5.0,
        'You, Me and Dupree': 3.5,
        'The night listener': 3.0,
    },
    'Michael Phillips': {
        'Lady in the water': 2.5,
        'Snakes on a plane': 3.0,
        'Superman returns': 3.5,
        'The night listener': 4.0,
    },
    'Claudia Puig': {
        'Snakes on a plane': 3.5,
        'Just my luck': 3.0,
        'The night listener': 4.5,
        'Superman returns': 4.0,
        'You, Me and Dupree': 2.5,
    },
    'Mick LaSalle': {
        'Lady in the water': 3.0,
        'Snakes on a plane': 4.0,
        'Just my luck': 2.0,
        'Superman returns': 3.0,
        'The night listener': 3.0,
        'You, Me and Dupree': 2.0,
    },
    'Jack Matthews': {
        'Lady in the water': 3.0,
        'Snakes on a plane': 4.0,
        'The night listener': 3.0,
        'Superman returns': 5.0,
        'You, Me and Dupree': 3.5,
    },
    'Toby': {
        'Snakes on a plane': 4.5,
        'You, Me and Dupree': 1.0,
        'Superman returns': 4.0,
    },
}


from math import sqrt


def sim_distance(prefs, person1, person2):
    si = {}

    for item in prefs[person1]:
        if item in prefs[person2]:
            si[item] = 1

    if len(si) == 0:
        return 0

    sum_of_squares = sum([pow(prefs[person1][item]-prefs[person2][item],2) for item in si])

    return 1/(1+sqrt(sum_of_squares))


def sim_pearson(prefs, p1, p2):
    si = {}

    for item in prefs[p1]:
        if item in prefs[p2]:
            si[item] = 1

    n = len(si)

    if n == 0:
        return 0

    sum1 = sum([prefs[p1][it] for it in si])
    sum2 = sum([prefs[p2][it] for it in si])

    sum1Sq = sum([pow(prefs[p1][it], 2) for it in si])
    sum2Sq = sum([pow(prefs[p2][it], 2) for it in si])

    pSum = sum(prefs[p1][it]*prefs[p2][it] for it in si)

    num = pSum - (sum1*sum2/n)
    den = sqrt((sum1Sq - pow(sum1, 2)/n)*(sum2Sq - pow(sum2, 2)/n))

    if den == 0:
        return 0

    r = num /den

    return r


def topMatches(prefs, person, n=5, similarity=sim_pearson):
    scores = [(similarity(prefs, person, other), other)
                for other in prefs if other != person]
    scores.sort()
    scores.reverse()
    return scores[0:n]